So why did this franchise get pushed away by Pokemon?

Digimon, when it started was relatively big, Digimon World and Adventure are still remembered rather fondly.
So what happened?
Well, the games all tried different stuff, sometimes rather unsuccessfully instead of building up a stable fanbase for them, since quality varied from shit to great.
Most of Adventure was improvised after the Myotismon arc, since they did not expect it to succeed and Adventure 02, while remembered fondly of those who grew up with it and did not rewatch it, partly killed the anime franchise by being terrible in almost every way.
The following season, Tamers then got rid of the previous cast, causing kids to drop it, although it is arguably the best season and a good anime by itself.
It also should be noted that the English dub for all of Digimon is atrocious, messing with the music, script, adding terrible puns and being censored to fuck.
The seasons that followed did nothing to revive the franchise.

Well, what happened on Pokemon's side?
Well, Nintendo had actual marketing strategy behind what they did, the Gameboy games were well marketed, had the whole collect everything thing going on as well as encouraging to fight and trade your friends, as well as being split in two to maximize profits.
They also got an anime earlier, which resulted in kids thinking Digimon was a rip-off. It is also quite possible they saw what happened what happened to Digimon with the cast switch from Adventure to Tamers, which caused them to forever use Ash and Pikatchu forever, which is why the Pokemon anime is so terrible and isn't allowed to go anywhere.
The games were always pretty much stayed the same and had small upgrades over time, while having questionable quality, considering a terrible amount of time is spent mashing A simply to get through the "story" and random encounters.

The two had similar themes, but handled them differently, one played it safe, the other didn't.