Convention goers are not staying in suites. Most companies will pay group rates for a regular hotel room, but certainly not Disneys suite rates.
Disney has convention facilities at Coronado Springs (a moderate) and that resort also has 40+ suites. I assume the CR convention facilities would tend to attract groups with larger budgets.
With WDW being such a popular family vacation destination, I assume many convention attendees take advantage of the ability to bring family members along. (I'm attending a conference at Portafino Bay in a few weeks and families are more than welcome.) Those combo convention / vacation families may embrace suites.
I wouldn't expect a big corporation to freely allow rank-and-file employees to book expensive suites on the company's dime, but higher-level employees or those working in lucrative professional occupations may not think twice. For many the cost would even be a tax deduction.