Listed vs games? Games vs expansions? I didn't go through everything and didn't even look at Sega series. It seems, by far, that for stand-alone games and stand-alone+expansions+dupes that king is the Sims series. Where I have 20 games, with an additional 41 expansions or "listings" aka variations.
If we are to talk about just entries, that probably is going to be some sports series. After looking at just PC, PS1-3 I have 39 releases of the EA Sports NHL series. I didn't even look at other sports series.
For things that matter, aka things I actually collect and play, the numbers are a bit lower.
13 for Quake
17 for Star Wars
11 for Ultima