Was it because they thought they had enough sitcoms for a block ? By the time TGIF came back shows like Malcolm in the Middle were getting great ratings and changing the game. Seems like abc messed up with this lol. Honestly abc could have kept TGIF going post Fall 2000 with other stuff they had, they lost all momentum by axing the block in 2000. It was literally too late when they brought it back. I honestly think the abc people saw The WB's neo TGIF lineup in 2001 and crapped their pants, literally this has to be what happened.

Neither Revivals of TGIF block where that successful but The Original TGIF era on ABC remains to be untouched to this day