It's tricky. Did you close the accounts? That will knock down your score. Making on time payments is the best thing for your score, but having credit lines open and unused is also beneficial. If you went from having a $5000 balance on $10,000 of available credit, to zero balance on $10,000 credit, to zero balance on zero credit, that can explain the swing. Closing accounts also may decrease the length of your credit history, if you close your older accounts.
However, if you did close your accounts, opening new ones will also hit your credit score twice, at least temporarily, since opening new lines is a minus, and new lines will decrease the overall average age of your credit.
You may help your score if you continue to use your credit cards and pay them off in full every month, and keep your average balance to less than 10% of your total available credit. The only real guaranteed way to raise your score is to wait, it will go up over time.
Remember that your credit score is just a crude prediction of your risk to the next lender you want to borrow from, and anything over 740 is going to put you in the lowest risk, best borrower category.
Here's an article for more information. https://www.experian.com/blogs/ask-experian/infographic-what-are-the-different-scoring-ranges/
