Every transaction destroys a small fee in XRP. When the network is busy, that cost rises, so flooding the ledger with junk gets expensive. That is the anti-spam job. The fee is not paid to a miner. It is destroyed.
XRP also sits in the middle of trades. The exchange can route a swap through XRP when that path is cheaper than trading two tokens directly. That is the bridge job. It is a tool for a better rate, not a guarantee of one.
Accounts hold XRP for reserves so the shared record does not grow without limit. Issued tokens are different: an issuer owes them, and that issuer may have freeze or clawback rights. Nobody owes you XRP in that sense. The supply was created at the start, and fees only shrink it.
Real example: the ledger’s own FAQ lists these jobs — payments, spam protection, and bridging — and says other assets can be issued on the same ledger. Source: XRP Ledger FAQ.