Maybe because the hotel programs suck, compared to the airline programs. I've got a few hotel cards, but I generally don't bother with them, for the following reasons:

1. As a leisure flyer who doesn't travel on business, it's just not possible to accumulate 20+ visits a year, which are necessary for any real perks. OTOH, it's pretty easy for me to score some sort of status with the airlines. I'm currently 1K with United, although I got it using the double miles promo at the end of last year (my actual BIS miles last year were 61K). Next year I should be either PremEx or 1K again (if they have another promo).

2. It's much easier to stick with one airline than it is to stick with one hotel chain.

3. I have *wood Gold (comped from Amex Plat), but it's about as worthless as a Southwest upgrade.

4. A hotel upgrade simply isn't worth as much as an airline upgrade! I don't spend much time in my room, other than sleeping, so a suite just isn't all that important. What's most important is a convenient location, a clean room, a hot shower, and a comfortable bed. The few perks that are important to me are free internet, free local calls, and free breakfast. And I'm more likely to get these at the LOW-COST chains! The premium product hotels are far more likely to soak me for these (just the opposite of the airlines). OTOH, due to the confining space of an airplane, the larger seat one gets with an upgrade is VERY IMPORTANT! Also, the better food and service, and free booze are more important when you're a captive audience.

5. I reserve most of my hotel rooms on Priceline. And hotel rooms there are often MUCH CHEAPER, frequently as little as 40% of even the cheapest web price! OTOH, airline tickets on Priceline aren't that much cheaper than I can find by shopping around and timing my flights when prices are low. And again, with dubious hotel perks, I'm much more willing to give them up in return for a huge Priceline discount!