Reasons why Dallas and DFW have more hotel options include;
1) It is a regional hub for finance and merchandising. If you work in the design field anywhere in the region, you will often have to travel to Dallas for sources and the large Merchandising Market trade shows. I've been at least a dozen times when I owned a retail store. When I renovated my Houston house, I also had to travel to Dallas overnight for showroom visits to places like Waterworks that don't (at least didn't) exist in Houston.
2) It takes advantage of a more central location and the huge airport to land large conventions.
3) It takes advantage of its location to host lots of large scale sporting events including 4 bowl games, 3 NCAA conference tournament championships, PGA events, etc...
4) It is less international and filled with a lot more folks from nearby places meaning it gets more frequent "friends and family" visitors.
5) It is a regional entertainment draw with things like a large amusement park that we lack.
6) It's an educational hub with two schools with lots of out of state students (SMU and TCU) and several large public universities in the region (UT-D, UT-Arlington, North Texas)
Lastly, Dallas has a reputation for glitz and glamor that Houston lacks. It makes it a safer choice for brands to test the Texas market. We've always taken a back seat and the rise of Austin isn't helping.
That said, Houston is improving in so many ways. For too many years we were simply ok with being a place people came to make money but didn't plan on sticking around. But the last two decades have seen massive improvements with quality of life issues that have made Houston so much better. The continued growth of the TMC, stealing away XOM, the planned growth for Rice, and UH's improving standing will all help. Additionally, word is out that Houston is an incredible place for food and art. I've met a growing number of people who have visited specifically for the Menil and restaurants. We should play that up hard.