5 stays or 15 nights in a year at Hyatt and you get Platinum status which includes free wifi (though Hyatt just made wifi free at all their properties). At Hilton it's 20 stays or 40 nights for gold but you can find a fast-track offer and get that status after 4 stays, or just hold certain credit cards (plus free breakfast, gym access, some upgrades, etc).
When hotels first started rolling out WiFi, charging made lots of sense. Most guests couldn't or wouldn't use it, and those who did would be happy to pay a little extra for internet on the go.
Things have changed now. Everybody uses WiFi, and it's available all over. A hotel charging extra for internet access is now almost like charging extra for lights in the room.
What makes it especially bad now is that fast cellular internet is becoming ubiquitous. People appreciate WiFi because it doesn't chew up their data plan, but they'll be ever less likely to pay for it.