what doesn't make sense about it?
One guy shoots & scores a bit more, has impressive straight line speed for his size, hits more & fights a bit. he doesn't bring much else to the table.
The other guy puts up more assists and points overall, is not a hitter or a big guy, but has impressive defensive numbers and has shown an ability to play well with top offensive talent.
Maybe you think the slight goal scoring edge, size & hitting make up for the drop off in defensive play & overall point production (especially factoring in TOI). I personally think it's close to a wash. It's like trying to compare a prius to a pickup truck. Both certainly have their value, just depends on your needs. Heinen overall has been the more productive player thus far in their careers, especially factoring in age. You better be sure the intangibles Anderson brings make up for the production difference if you swap them.
Personally I'd prefer to have both. I like that when Anderson is scoring goals they are mostly at even strength. That bodes well for him playing with Krejci. He also hasn't had a long-term center as good as Krejci. I think they'd be a really good fit together, but I also think Heinen is a versatile guy who is underrated here.
A lot of people are talking about trading Heinen for Anderson as if we'd be trading an unproven prospect for a proven guy in his prime, but the reality is that both guys still have a lot left to prove and have each had about 1.5 seasons total of playing up to their potential.