They can't if the protocol doesn't allow it.
Otherwise it will be regular centralized storage providers with IPFS bolted on top for one or two geeks who care about it.
Because IPFS links are not URLs, it works on a different paradigm.
The chance of somebody storing your HTTPS files and IPFS files is the same. Users pay hosts to keep hosting them. With IPFS, if the user stops paying the file hosting service, another user can pick up the slack without the link becoming dead.
Too much faith in someone picking up your files when a centralised host goes down. This is an important detail that for some reason is always dismissed by IPFS proponents.
But if another party is interested in the file, they have the option to persist the file regardless of what the original party and centralized services choose to do.
What does IPFS bring into the picture apart from "oh yeh, there's a near-zero chance that someone will keep hosting your file"?
1 - A content addressable URI protocol that allows you to locate a file without linking to a singly-owned and named server or host. This is not the case with HTTPS URL protocol.
2 - Open source clients where multiple parties, including competing parties and individual users, can all simultaneously and permissionlessly peer-to-peer host an asset behind the content addressed URI.