That’s an issue with the choice of network, not the token. They could be sending USDT/USDC as payouts on the same ETH network… and transaction costs would be volatile… and there would be minimum fees… and L2 options to try to avoid those fees.
When Storj can afford it, they definately could start using stablecoins. They wouldn’t switch immediately: because there are a lot of STORJ tokens out there and people would scream if their value went to zero overnight. But SNOs can already swap their payouts to stablecoins if they’re concerned about token values… so it I don’t know if I’d say they should do it. If SNOs want to hodl stables… they’re already hodling stables 
SNOs can always do what they want. Hodl. Sell. Burn. Whatever. After being told for years that STORJ isn’t a token they should expect to increase in value… they could still hodl it. I think selling is a better option (or like you’ve mentioned: swapping to a stablecoin).
Storj still does not really have the money to pay the SNOs. They hope 2026 will be the year they really have the money to pay the SNOs. Until then: they’re relying on the remaining treasury tokens (while they ramp up monthly token buys - because eventually they’ll need to buy at least 100%).
As of today Storj isn’t buying all the tokens needed to send to SNOs (just a small amount): they aren’t profitable yet: they can’t afford to do so. So still using treasury tokens for now does make much sense.
I hope they become profitable soon. And I’d be fine with stablecoin payouts one day. But if they’re telling the community they can’t afford it today… and they’re looking for ways to sustain the value of the STORJ tokens they still have in their back pocket: I understand those ideas as business decisions.