This is not necessarily the case. On some exchanges, there was / is a competitive voting system. The project team can encourage the community to vote on the listing of the project asset. In case of victory, listing will be free (or almost free). In 2018, there were at least two such exchanges.
They list for free, but they still need to spend money to hire market makers to create liquidity for their tokens. Either way, listing on such major exchanges will undoubtedly require a lot of money.
At large exchanges, listing always requires a lot of money, of course they can add a promising token for free or by voting.