Most Tether is on Ethereum:

https://wallet.tether.to/transparency

Most Tether volume is also on Ethereum, as the article above notes:

>Notably, the total value of tether transacted on Ethereum is still larger than Tron, signaling that primarily smaller transactors are migrating. Meanwhile, parties executing larger transactions who can presumably afford higher fees seem comfortable continuing to use Ethereum.

The big issue is that there's simply no space on Ethereum for smaller transactions. Hopefully some of this volume will migrate to Ethereum's zkRollups, namely Loopring and zkSync, which increase Ethereum's maximum throughput from 30 to 3,000 ERC20 token transfers per second.