Basically because X-Women are strong in personality and power.
In other works the most powerful are men.
In the x-men (I include New mutans Gen X and others) the most powerful are the women.
The most striking cases of the x-woman are the most powerful of their groups, we have it very clear if we focus on Jean Gray, Rogue in Storm and Magik, Monet just to name a few.
And in some of their best exploits of power they have saved the planet litterally thanks to their powers (Rogue has repeated this feat some times XD).
The X-Women have a strong personality, and they are of very high level of power, and Claremont must be thanked in part.
The truth is that the unlimited potential of power comes from the side of Jean, not Cyclops, which as we know is a mutant not very powerful, but rather normal, and Havok the same, only Vulcan broke the mold.
And by the way Jean is even more powerful than Rachel, and that Rachel has the crossing of X genes, which according to Sinister "they give very powerful mutant", but in the 3 "children" of Jean and Scott I do not think it's chance that 3 have only the Jean Gray powerset, and all 3 are confirmed omega level.
Another Example Scott had a daughter with Emma Frost, (Ruby Summers) and she took off the powerset of both parents, and not at all seemed an especially powerful mutant.
So the root of power and unlimited potential comes from Jean's side really.
Alex might not be an omega mutant but he's certainly no wimp and much more powerful than Scott, but the Summer side does contribute more than just simple dna...
Is it just me, or of late...
... has there been some calculated correlation between the first 3?
Going back to the OP's topic question directly, I recall one documentary that put it quite succinctly. When it came to the X-Men & their female characters, they didn't just contribute & play supporting roles in stories, they WERE the story. Entire arcs would revolve around them, to the point where they became absolutely INTEGRAL to the proceedings, and became the biggest 'face' for the franchise this side of Wolverine. And it can be evidenced to this day, especially with their most recent offerings, from just this year:
I think it is possible to make sense of it, as in, Jean's mutation is being able to be a perfect host for the Phoenix. It isn't her telepathy or telekinesis what makes her worthy (otherwise, Exodus for example, might be worthy too), she is genetically a perfect Phoenix host who can choose to use the power of that cosmic entity at will.
Jean rejected the Phoenix in Resurrection, but if she changed her mind, the Phoenix would go flying through space at light speed towards her. The Phoenix is her privilege. Not herself.
Awwww... it IS awesome, tho, I agree. And they're all dressed pretty modestly, too, with no cheesecake poses. Covered up for the most part, with only 'Yana & Clarice showin' any sort of skin. That's GOTTA be an achievement, in & of itself. Sure, they're form fittin', but so are the guys' uniforms/outfits/costumes.<Whole>
<Bunch>
<Of>
<Awesome>
<Covers>
Now all we need is covers from 2018, for the triumvirate of:
... Emma, ESPECIALLY Dani, & Monet, to grace with their presence.