Solana has a company behind it, Monero has a couple foundations I think but it's mostly a bunch of independent devs behind it (some of which, like Fluffy Pony, definitely have enough money to spend on marketing if they wanted to). It's the difference between something that is pseudo-decentralized and actually decentralized.

I don't see how you can implement smart-contracts in general on Monero because it's not programmable. You can write small arbitrary messages via tx_extra and in theory some other chain that looks at the Monero chain could read that, but because tx_extra messages are direct-writes and aren't automatically encrypted using the wallet keys or anything, there is nothing special about them besides them being immutable. In fact in some ways tx_extras could contribute to deanonymizing the chain if it created correlations between ring signatures, and Monero devs have discussed removing it several times.

There's a question of whether Monero itself could be extended to be programmable and actually do things with those messages, but I'm guessing the answer is probably no because it would bloat the chain and have questionable value (right now Monero is "unixy" in that it does one thing and does it well), even if it were possible to do.