While in Bitcoin you can offload older utxos to a slower memory, because the access pattern is “utxos die young”. Also, utxo set grows much slower or even can be stable (“1 utxo per person”) while tx volume grows forever.
Bitcoin scales way better than Monero or Zcash (that has the same requirement to store all “nullifiers” to prevent double spending).
That term is misleading and implies actual RAM-type memory is needed, which is untrue. Monero scales quite well using a database on SSD up to transaction rates far in excess of anything Bitcoin can or will realistically handle now or any time soon (certainly hundreds and possibly thousands of tx/sec).
Likewise the total data that needs to be stored grows slowly at realistic tx rates, roughly 80 GB/year at 10 tx/sec. That's similar to the rate of growth of the bitcoin blockchain (unpruned) and well within the hardware capabilities of both existing cheap SSDs and even more so the visible trajectory for future cheap SSDs.