You see, back in the 70's, musicians got it into their heads that mass = sustain and fat tone, and that resulted in "innovations" (ymmv) like high mass bridges, brass hardware, and as you've discovered, 900lb hard ash bodies. CBS/Fender, in a quest to fix things that weren't broken, hopped on this bandwagon - on top of cutting costs at the expense of build quality (after all, sustain and tone have everything to do with mass, not quality parts and construction, right?) This is not to say Fender didn't produce some good instruments in this time period, but those were the exception, not the rule.
This led to Fender circling the drain until the employee buyout in the 80's, and not truly recovering until the late 80's/early 90's, when popular indie and grunge/alternative bands were seen playing vintage Fenders because that was what they could afford (and if I'd only been born 10 years earlier, I too could have taken advantage of pawn shops being littered with dirt-cheap vintage 60's Fender basses...).