You can easily swap L-USDT to Tron or Ethereum addresses from inside Aqua wallet, so they don't need to have all centralized exchanges with L-USDT listed directly.
And I wouldn't even hold USDT on any blockchains long term, there is always risk with them losing peg because of potential ban or regulation change.
That is convenient, sure. Some may find it practical. By the way, what are the commissions of such swaps? I'm not very familiar with Aqua wallet, but as far as I understand they use Boltz exchange for those swaps. So they sure got to cost something.
But overall, can we say that USDT on Liquid is successful? They minted first USDTs on Liquid in 2019, almost 5 years ago, and yet the volumes, according to the official Tether site, are still quite low:
Total Authorized $36,561,000.00
Net Circulation $17,211,849.00
While for example on TRON USDT was introduced only at the end of 2021 and the volumes are totally different, 1000 times bigger:
Total Authorized $58,816,920,368.94
Net Circulation $57,940,630,837.05
In comparison to Tron, USDT on Liquid does not look like a success at all.