The least of it was amnnesty (bad enough). The magic bullet was that it would have allowed another 100-200 million more immigrants into the country to "do the work that Americans aren't doing" for big business.
That, in short, is the answer to the original question. The bill contained provisions to allow lots of low wage immigrant labor to keep the PPI low and citizenship provisions to enlarge the voting rolls of the Democratic party.
Unfortunately for the proponents, there was another Left/Right coalition that defeated the bill. Labor did not like the wage-lowering effect of massive and unregulated immigration. The rank and file Right did not like the amnesty-like provisions of the bill. Neither the labor nor the rank and file Right trusted the Congress to actually implement the border control and labor enforcement provisions of the bill. The same kind of promises were made during the last Congressional amnesty in the mid 1980s. Those promises were abandoned so quickly that it was obvious the promises were only made to get the amnesty passed. We remain convinced the same would happen with the new bill.
Myself, I might be willing to accept the guest worker program and a citizenship track for some illegal aliens, provided they pay some sort of penalty for entering illegally in the first place. I WOULD NOT accept such a program until Congress first creates and funds an infrastructure for border security and workplace enforcement and the executive branch implements such a program effectively for several years. The Federal government has proven they cannot be trusted to implement both at the same time.