There are many advantages. For example, with the amount of training I do, I’d need a separate rear wheel with a training tire and a cassette. (I don’t want to use up an expensive tire on the trainer.) So price-wise, that’d be more expensive. And the ride feel with a direct drive trainer is more consistent.
For comparison, I got my Elite Volano used for $200ish. The cassette cost another $100 (SRAM cassettes are very pricey in Japan). This year I had to buy an XDR driver body from Elite and Force 12-speed cassette. But again, if I had a wheel-on trainer, I would have had to buy both, too.