It is because he was only getting 6-7 mins a game with Arizona, and there was about a week or so when he was playing with both of them, before they moved Kane up to Toews' wing.
No he wasn't. I don't know why people make things up that are so easily debunked. Strome was playing 11:03 a game at ES with Arizona and he's played 14:16 with Chicago. That's roughly 220 minutes in AZ and 555 minutes in Chicago. About 350 of those 555 minutes have been with Kane (63% of his ES TOI while in Chicago).
He's played roughly 775 total ES minutes this season. For Strome to have played 45% of his total ES minutes with Kane in just the first 20 games or so, he would have had to play 350 ES minutes in those 20 games which is 17:30 of ES minutes per game (Even Toews only plays 15:47 at ES). That's not even possible considering he played around 17:15 in total TOI during those first 20 games and that's including the 3 minutes a game he plays on the PP.
I'm sorry but numbers don't lie and simple Math would say that's literally no chance possible he has only played roughly 20 games with Kane and the rest is made up by overlapping shifts.
Anyway, I think we're caught in the weeds here because it doesn't really matter when, for how many games, or how he got to this many minutes with Kane. The FACT remains, Strome has played significantly more with Kane and Debrincat (not necessarily together) than anyone else and I'm talking more than double the minutes for both of them compared to the next closest linemate.