The reason was that you could spit the blocks out under heavy braking in think.
Not suggesting that blocks are good on the front axle (or elsewhere), but aren't the spring assemblies through-bolted/doweled? I feel like there are locating dowels or bolts to keep everything aligned. I only used blocks once on an S-15 rear axle (for lowering), the blocks had corresponding dowels and receiver holes. Provided the u-bolts were properly installed and torqued, everything should have stayed together (in theory).
