[Mick]

I repeat this over and over. For some reason, it never seems to "take". Rosen was dead set that he was going to start as a freshman. That was a requirement for him to get to the NFL as quickly as possible. Shaw wouldn't guarantee that. End of story. There are undoubtedly other factors that may have led Shaw not to offer, but the fact is Shaw wouldn't offer a guaranteed starting position as a freshman.  Rosen made it clear that was a disqualifying issue. No point in Shaw making an offer that won't be accepted, dream school or not.
Mora did make such a guarantee, Rosen enrolled early at UCLA (which he could not have done have done at Stanford) and started as a freshman. Rosen has stated several times that starting as a freshman was a requirement for him. This is not a secret.

Rosen did indeed start all 13 games as a frosh.  Here's the language from his profile:

Starter in all 13 games … Became first Bruin true freshman to start a season-opener at quarterback … Set numerous school marks - most consecutive passing attempts without an interception (245); most passes attempted in a game (57 v. Wash. St.); most passing yards by a true freshman in a game (399 v. Cal); most passing yards in a season by a true freshman (3,670); most 300-yard passing games in a season (tied-6); most touchdown passes thrown by a true freshman (23); most touchdown passes thrown by a true freshman in a game (3-tied); longest pass play by a true freshman (70 yds); most completions in a game (34 v. Cal); most passing attempts in a season (487); most passing yards per game in a season by a true freshman (282.3) … Threw for 300-yards in games v. Nebraska (319), Wash. St. (340), Oregon St. (333), Cal (399), Stanford (326) and Virginia (351) … Had three scoring passes in games against Nebraska, Cal, Stanford and Virginia … His 410 yards of total offense v. Washington State ranked No. 9 on all-time school list … The Sporting News' Freshman of the Year … USA Today 1st team Freshman All-America selection … The Sporting News' 1st team Freshman All-America selection … FWAA 1st team Freshman All-America selection … Pac-12 Conference Offensive Freshman of the Year (coaches) … Pac-12 Newcomer of the Year (AP) … Honored in New York after being selected as one of five recipients of the 2015 NFF National HS Scholar-Athlete award … Presented John Boncheff, Jr. Memorial Award for Rookie of the Year and the Captain Don Brown Memorial Award for Most Improved Player at the annual team banquet … Enrolled in January of 2015 and participated in spring practice.

[Mick]

I repeat this over and over. For some reason, it never seems to "take". Rosen was dead set that he was going to start as a freshman. That was a requirement for him to get to the NFL as quickly as possible. Shaw wouldn't guarantee that. End of story. There are undoubtedly other factors that may have led Shaw not to offer, but the fact is Shaw wouldn't offer a guaranteed starting position as a freshman.  Rosen made it clear that was a disqualifying issue. No point in Shaw making an offer that won't be accepted, dream school or not.
Mora did make such a guarantee, Rosen enrolled early at UCLA (which he could not have done have done at Stanford) and started as a freshman. Rosen has stated several times that starting as a freshman was a requirement for him. This is not a secret.

Rosen did indeed start all 13 games as a frosh.  Here's the language from his profile:

Starter in all 13 games … Became first Bruin true freshman to start a season-opener at quarterback … Set numerous school marks - most consecutive passing attempts without an interception (245); most passes attempted in a game (57 v. Wash. St.); most passing yards by a true freshman in a game (399 v. Cal); most passing yards in a season by a true freshman (3,670); most 300-yard passing games in a season (tied-6); most touchdown passes thrown by a true freshman (23); most touchdown passes thrown by a true freshman in a game (3-tied); longest pass play by a true freshman (70 yds); most completions in a game (34 v. Cal); most passing attempts in a season (487); most passing yards per game in a season by a true freshman (282.3) … Threw for 300-yards in games v. Nebraska (319), Wash. St. (340), Oregon St. (333), Cal (399), Stanford (326) and Virginia (351) … Had three scoring passes in games against Nebraska, Cal, Stanford and Virginia … His 410 yards of total offense v. Washington State ranked No. 9 on all-time school list … The Sporting News' Freshman of the Year … USA Today 1st team Freshman All-America selection … The Sporting News' 1st team Freshman All-America selection … FWAA 1st team Freshman All-America selection … Pac-12 Conference Offensive Freshman of the Year (coaches) … Pac-12 Newcomer of the Year (AP) … Honored in New York after being selected as one of five recipients of the 2015 NFF National HS Scholar-Athlete award … Presented John Boncheff, Jr. Memorial Award for Rookie of the Year and the Captain Don Brown Memorial Award for Most Improved Player at the annual team banquet … Enrolled in January of 2015 and participated in spring practice.