3 PIPs within 5 months

I was a new hire at Amazon and got first PIP at my 60th Calendar day of being hired due to "under-performance". Ironically during the 60 days, my manager was off for two-week vacation. The days we actually worked together are only more than one month before this PIP.

I reported this to Jeff and then HR changed the PIP to a two-week development plan. After two weeks, the manager gave me the second different PIP. After one month, the manager still wanted to fire me. I disputed with HR and they gave me a third different PIP at my fourth month.  I did not sign the third PIP and then quit at my fifth month.

So, in total, I had 3 different PIPs and 1 Dev Plan within 5 months. Even if they don't like my work, why do they keep creating different new PIPs to find excuses to fire me instead of actually finding anything really wrong with my work?