I do play both as well. been playing 40K since 3rd and infinity since the start.

Like anything else to much of a good thing is a bad thing. I diversified my gameplay because after a decade or so doing 40K non-stop it leads to burnout. infinity is a totally different feel and that's refreshing.
I personally still also play kill teams/combat patrol for 40K but we still play a slightly modified 5th ed because it allows a lot more freedom in building your force(and I enjoy the rules set more) and the XP progression/wound chart adds some enjoyable depth.

The real difference between normal 40K and infinity comes down to just a couple factors-cost & terrain with only about 2 trays and about $200 invested I have enough haqqislam units to field 4 noticeably different infinity armies with a few unit swaps. 40K is incredibly more expensive because of GWs pricing and the need to field more than 10 models to make an "army" like in infinity. the other side is terrain. infinity requires ridiculous amounts of terrain to make a viable battlefield because of the reaction mechanic. don't get me wrong the tables look fantastic and there are several companies like micro art studios and antenocitis workshop that specialize in terrain for infinity, but it has a much higher investment cost for terrain than 40K.

I have negated to cost of playing 40K myself by switching over to playing 8th edition at epic 6mm scale via merely reducing movement and ranges by half. In the 28MM range I have also stated playing dust 1947 a lot more as it is a mix of both 40K 8th edition and infinity but with an alternating activation mechanic. negating much of the "go first=win" problem that has plagued 40K.

Hope that covers what you are looking for.

example infinity terrain-

Epic scale 40K table-