Hmm weird. Since I started using it a few years ago bulk selection actions never appeared with Sam’s Simple Theme. While working on some other theme component a year or so ago I did run across a code snippet that made it start working, but I either removed it by accident or it stopped working with an update.
The only possible difference I can think of is that I’m on the stable branch, but like I said this has been a long-standing issue for years for me.