The problems with this approach

The development cycle was too long
New features could sit for years

The feature freezes never held
Some "important" changes would always slip in

"Stable" kernels stabilized slowly
Vast amounts of changes to shake out
1.0 -> 1.1:  34 days
1.2 -> 1.3:  97 days
2.0 -> 2.1: 113 days
2.2 -> 2.3: 105 days
2.4 -> 2.5: 321 days