I think their anime is better, it has a more mature theme, better designed characters maybe? They also have tons of iconic characters *cough* cough* and they culturally more prevalent in society. Let's throw in Monster Rancher for good measure.
Considering the whole pokemon franchise is heavily supported by their ability to put out popular games and Digimon failed to do so, it's pretty understandable.
I mean, the biggest Digimon game I remember was Digimon World, which almost had something really going for it, but had too many flaws to ever hit big. It was followed by 3 "sequels" that tried something different each time, and each time was progressively worse in terms of gameplay and overall quality.
If Digimon had stuck to the Digimon World template, they could have revamped the series games and revived interest in the Digimon overall, but they just didn't.
"They don't think it be like it is, but it do." - Oscar Gamble Should have. Should *******have.
A combination of no big marketing and the fact that the quality of the Digimon games are dubious. Digimon does enjoy more success in Japan, where they had multiple more toys and digital pets (of much higher quality than what Not Japan had), and there's still an anime series with games being produced.
Overall, the games are just of lesser quality. Digimon World 1 was a great game, but very rough around the edges, and the NTSC version was plagued with bugs. DW2 was a roguelike, but required a lot of grinding and much of the game was "Did you fill up your inventory with ten items to remove an obstacle? TOO BAD YOU NEEDED ELEVEN HAVE FUN GOING THROUGH THE LAST 23 FLOORS AGAIN!". DW3 had a lot of grinding, a very slow battle system, depending on your region the game would lock you out of countless things after a certain point, etc.
I could really go on, but there has yet to be a Digimon game that can match Pokemon in quality, or indeed one that was just plain good without any major or apparent flaws. Pokemon itself has a formula and way of doing things that could have been used as inspiration, but anything like this would just result in people furious that "Digimon is copying Pokemon agaaaaain". The games themselves never even really had a niche like you could claim with Monster Rancher.
"Murder of the living is tragic, but murder of the idea is unforgivable." - Janus, speaker of the synod
I played Digimon World 1 and I'll be honest, I loved that game. All my friends did. We even had local tournaments (I used Metal Mamemon). I tried to love DW2 and DW3 but everyone in our group had the same sentiment, DW2 and DW3 had no soul (I don't want to expound on that). We eventually tried to go back to DW1 but it felt like we already squeezed out every bit of fun from that game. Controlling only one digimon, IMHO, was its biggest flaw. I mean, every 5 hours (I can't remember exactly), your 'mon "dies" and it feels like you're starting from scratch again. Training your 'mon, battling wild 'mons, and potty training starts to become really really tedious. At least if you can control two or more, when one of your 'mon dies of old age, you won't have to go back to square one. You can use the "elder 'mon" to help train the new egg, etc..