It's possible to have more than one reason for getting $75 billion from public markets. Paying off $20 billion of loans from people you don't want to owe money to (who, as far as I could tell, SpaceX borrowed money from to pay off people you really don't want to owe money to) and getting a really big number associated with your name are not mutually exclusive, and from Musk's previous actions (getting large compensation packages approved by conflicted boards) he obviously does want that number.