The ab initio program dilutes pilot pay. We are paid commensurate to experience. We are paid based on what we expect we are worth. A 40 year old believes they are worth a lot more than a 23 year old just happy to sit in a shiny jet. There are plenty of 20 year olds who would PAY to sit in that seat. BIG difference.
Folks with decades of experience also understand the importance of unity in a union (well most anyway). Ab initio is just a way to control pilots from when they are the most naive and ignorant.
And also, while some pilots got hired into E145's with around 300 hours, it was never "most".
FWIW, I interviewed with JetBlue after 17 years from my first solo and was around mid-level age in my interview group.