With the Rays and its treatment of young talent, it’s financial repercussions mixed with in-depth analytics.
The organization is certainly going to do everything in its power to keep Shane and other young studs (looking at you Wander) under team control for as long as allowable by keeping them in the minors - even when they should/could be getting those same innings in the majors.
That said, you can certainly see the advanced analytics coming into play as well with the young pitchers (SM, Glasnow, etc.) being limited to 60-70 pitches in the beginning and then lengthening then to 80-90 as they progress. My guess is they’ve discovered that once a guy gets over 60 pitches then he’s not as effective (makes sense, as the third time through the lineup you can usually see a spike in batting avg, runs allowed, etc.) and then they go to the pen.
This allows the young guys to put up artificially skewed better numbers, thus driving up their value to the rest of the league once they become trade bait. Only within the last year or two prior to free agency/trade time do you see the pitchers get stretched to 90+ pitches per game and 150+ innings for the year, to prove these guys aren’t a fluke - which usually happens (look at Snell and Archer) and results in big contracts for the guys leaving and good young talent in return for the trade.
TL; DR...the Rays know exactly what they’re doing, but as a fan, I’d like to see the young guys develop in the majors rather than the minors, as it’s more exciting and better for the players careers financially.