They probably have the capability (and infrastructure) to expand but they are taking their time by evaluating options and scenarios. There is another possibility "less is more" therefore if that is what the eXch team are trying to do by focusing on a core handful of coins it is working because they have an excellent reputation and provide a brilliant service. Maybe adding more options will damage their reputation especially if there are fluctuations in fees but that should not really be a factor in the decision.
About TRC-20 stablecoins, they have already written in this thread in November that they're perhaps interested, see here. They're however generally sceptical regarding Tron.
As for other Ethereum alternatives with stablecoins, in the same post they wrote about Polygon too (they were considering adding it, but sceptical due to the high fees close to Ethereum's, which may have changed), and this post probably means that they're not eager to add Avalanche, although the post is related to a bridge, not to stablecoins.
(I answer here just because I remembered these posts exch made in November. Of course their policies may have changed and I actually would also love some new alternatives.)
As for other Ethereum alternatives with stablecoins, in the same post they wrote about Polygon too (they were considering adding it, but sceptical due to the high fees close to Ethereum's, which may have changed), and this post probably means that they're not eager to add Avalanche, although the post is related to a bridge, not to stablecoins.
(I answer here just because I remembered these posts exch made in November. Of course their policies may have changed and I actually would also love some new alternatives.)
