LOL...not only are you wrong but it lacks a modicum of logic.
Session players were paid and were light years beyond the BB's skill set. Even Brian Wilson acknowledged the difference in quality.
Yes, actually listen to the Wrecking Crew themselves talk about it. Yes, there was a cost to hiring them, but it did save money, because the session musicians would get things done in one take.
Those sessions players said themselves, often those bands could do themselves, but the difference was the session musicians did it in one take, while the band would do multiple takes. The record companies wanted it done in one take. That saved more money than the cost of hiring the session players.
Remember, they did multiple sessions i a single day. They didn't make that much per session.
I've heard members of the Wrecking Crew say that many times.
It also doesn't mean they were the absolute best players.
Look, at Hal Blaine. He was a machine, and he would give you the same thing every session. That works both ways. He gave you a consistent performance, but he didn't give you exceptional creativity or soul, either.
You can look, Steely Dan on exactly one song. They cared a lot who was playing, and they cud get more from Steve Gadd, Jeff Porcaro, or even Rick Marotta.
So, yes, they absolutely did it to save money.
And not all musicians have the same skillset.