Two points come to mind:
- We now have a young and fickle electorate, who might change their votes in the next election if they aren't satisfied with the manner in which the incumbent party performs.
- Being able to control a microlending organization like Grameen would allow a political party to apply financial pressure on borrowers to influence their votes.
It's quite possible that vanity and pique (not getting the Nobel herself, Yunus attempting to start a third party) played a role, but one also needs to look at the calculus of power.