ELI5: When is rolling in the closing costs worth it when refinancing a mortgage?

I read in many places that it's always better to roll in the closing costs into the new loan amount and I'm not able to get my head around it. Say, my closing cost is $5000 and I pay it upfront then I don't have to pay 6% interest on that amount in the EMI. Now suppose I rolled it in and if I refinance again after an year then it will cost me, say $4000, then it will just add to the previous $5000 and my principal will be $9000 more overall. So now I have to pay interest on the extra $9000 that got added to the life of the loan. In the long run I don't see how do I get ahead if I roll in the costs when refinancing? It looks like the banks would make more money in the long run.