I think the combination of lower-surface pressures surrounding the storm and the flat pressure gradient inside the storm itself (which are not necessarily directly related) are causing the underwhelming wind speeds so far. Wilma seems to have a very large radius of tropical storm force winds for a cat 1 storm, indicating that the system has not really wound up like a hurricane normally does. That will likely change if it keeps deepening like this. It may always have somewhat lower winds compared to what you would expect because of the surrounding below-average pressure field, but it still has a lot of tighening up it can do.