I can give you my reason for that ...
As reported on another thread here, I received a gift card to buy a subsidized phone from my carrier at a very good price, and the main product offered was the S5.
I spent most of the morning in the shop, testing and "tasting" the S5, undecided about what to buy (the alternatives were Lumia 1520 and LG G2). I was very tempted .... but I finally gave up with it.
Screen and form factor are very good, but build quality is just meh, and I really can't stand that back cover. What finally made me decide against it was touchwiz and bloatware installed on it....
I don't "hate" Samsung, but I'm very disappointed ....