I've been trying to learn to run this game since I just got the anthology and the slide made it my favorite in the series(even though most people say it's the worst) but my question is why isn't it on the list for times anywhere? I've found a time for hard in speed run archives and runs on youtube but nowhere current to post times.

Frankly because no one runs that game. Metal Slug 4 and onwards are pretty dead. Most runs you will probably find on youtube the game will be done on emulator, which are pretty incomparable vs console/port releases. The only non-emulator time I can think of is Uyama's run on SDA, which is literally a decade old by now.

Added. please use it freely.