Puck does get picked, but not as often as Tide. Soon there will be 100 heroes in the game, that would mean that for every hero to be evenly picked you'd see every hero in one out of 10 games. That's not a lot, and with the amount of carries and hard carries in the game that isn't even remotely possible within the confines of the meta-game. Tidehunter can lane well in any position except jungle and solo mid, while Puck demands a solo lane. Flexible heroes will always get picked more often just because of drafting strategy alone. Niche heroes will always get picked less because there's more options for their position. There aren't a lot of good support heroes, so the good ones get picked a lot because most of the time a team wants to pick one or more of them.