I guess that is simply because they prefer shitcoins to BTC, and they are more inclined to sell it to people rather than BTC. I do not know how true it is that Ethereum is gaining grounds on BTC in regards to institutional adoption, but what i see in the news more often is BTC adoption by institutions and nations as well, i don't see much or anything about ETH, or maybe i am the one who isn't looking well enough.
ETH can be controlled better and watched over, imo, and BTC takes the spotlight each time anyways, that's why we don't look at the news about it, because it doesn't interest us as much as stuff happening with BTC adoption-wise..