I think one of the reasons is that we don't develop enough high potential homegrown players (MVP/HOF). A local player selected for the NT brings in a lot of merchandising (between 15 and 20% of his salary). It seems that there has been a recent change for foreign players also in their NT and that the return on merchandising is now almost equivalent.
Here's an example:
My PG Victor Laurent, selected for the French NT and one of the league's top 10 passers, generates $74,000 in jersey sales.