I know, but having separate accounts within the interfaces of each site can be helpful. If I have a Mastodon account, I know exactly how my posts are going to look and act on Mastodon. Same goes with Lemmy and Kbin.
I also have access to features on one service I wouldn't have on others. Some posts are easier to view and access from a different site or instance. Kbin doesn't have any mobile apps yet, so I use my Lemmy account when I want to access fed on mobile.
Lastly, sometimes I'm just in the mood to use one site over the other. If I'm in the mood for more Twittery content I go to Mastodon. If I'm in a more Reddit mood, I go on Lemmy. If I want to do both at the same time, I use Kbin.