Remember that a key point of legislation is to carve out earmarks for your buddies without upsetting the general electorate too much. Version control would let the public know who's staffer inserted which earmark. The loss of plausible deniability might bring the whole system down. Without being able to feed your special interests, how would you ensure that you keep getting reelected each year?

I just read a particularly devastating critique of the quota system/gender pay differences in Thomas Sowell's latest book. His point (backed with copious evidence) was that the differences in outcomes is almost entirely explained by the differences in interest. Some careers require so much dedication that a few years away (raising kids for example) or shorter work weeks severely impacts your competitiveness. Folks who want to have a life outside of work tend to avoid these careers; why shouldn't we let individuals make that decision for themselves?