You mean ICO projects? I also noticed this, that some ICOs left Stellar in favor Ethereum (FlipNpik for example). I don't know why, because Stellar look like working more faster than Ethereum. May be because users want not participiate in Stellar ICOs and register new wallets or developers just afraid that they can't raise money selling tokens on new blockchain...
Wasn't there also some project that left Eth and moved their tokens to Stellar? Yea, Kix. Seems they have tokens on both now though.
Yes, this is possibly was as well. As far as i know one project wanted to move their tokens from Ethereum to Stellar blockchain (this was Rate3). But I don't know they did it or not as i lost interest to this project. How many existed tokens in total Stellar blocckchain have so far? They are trading on exchanges without problem (stellar tokens i mean) ?
I can't say how many Stellar chain tokens run on exchanges, but they can all be traded on StellarX without issue.