Easier maintenance in both short and long term. Compare how many spare parts you would need to stock to keep an M1A running vs a Bolt gun.
I ain't buying that one little bit. I got my M1A in 1977 and have been shooting it quite heavily since. Shot for the NG until I retired in '92 and still shoot it in competition, which requires quite a bit of practice besides the matches.
I have had to replace a couple barrels and stretched out slings but that's it.
The M1As hold up quite will.
As the M21 in SE Asia they actually spent less time in the maintenance shops then the Marines M40s of the period.
If you like other rifles fine, but don't blame it on the M1A needing heavy maintance.