Why does Yasser Seirawan hate 1. e4?

He thinks its only the 4th best move.

Because all his success came from playing 1.d4 and especially 1.c4.

1.e4 killed his father.

Seirawan played the Caro-Kann against 1. e4 really liked it.

As White he often played the English and 1. d4 (which often transpose) and sometimes he played 1. Nf3. These three moves often transpose and will often be similar. 1. e4 is different, and I don't think he played it much, or liked it very much.

But anyway, just because he thinks it is White's 4th best move (I think he might have actually said it's his 4th favorite move), that does not mean he "hates" 1. e4. BTW, he was being serious I think, but was only voicing his preference.

Everyone has some preference or other for opening move.  Allied with that are moves they don't like too.  I don't like 1. d4 just because I've never learned much about wht to do next!

Personal preference.  There are plenty of top players, both in the past and currently, who are better than Yasser ever was and primarily play/played 1.e4.  To each their own.

Also Yasser's hero - Bobby Fischer - was an e4 player.

  I think it is very rare when any player is equally comfortable with both e4 and d4.  I have always prefer d4 but i think most players (with white) prefer e4

He has a great book on openings in which he explains his own choices, that came from a desire for more control over wild tactical battles. He found that d4/c4 suited that desire. That's all.

He was a late bloomer in chess and didn't have time to learn the latest novelty in the Najdorf or Breyer so he opened 1.c4 in just about every tournament game with white. This allowed him to get through the opening safely with a decent position and beat his opponent's because of a better understanding of the 1.c4 setups.