I played Magic casually for awhile and then got pretty involved in the Pro Tour scene, in which the qualifiers have similar structures to 100-person MTT shootouts.

The elements that cross over are many:
-Probability Theory
-Game Theory
-Hand Reading
-Strategic Thinking (usually many turns ahead)
-Opponent Profiling
-Game Selection (for constructed events, building the right deck against the field)

There are undoubtably more that I did not list, as well. There is the monetary aspect of Magic's Pro Tour which is not usually enough to fund a above-average Magic pro for a year's salary, so many of them switch to a parallel game that they CAN make good money.

Backgammon shares similar overlap, as you probably know.

Also, the majority of Magic players are young male adults, ages 17-28. This is the most sought-after demographic in the United States (and likely the world, but I cannot comment so broadly), and many of them also enjoy video gaming, which partially overlaps with poker.