I'm with you here.
Characters need to have some kind of relationship and to humans there only a few natural positions relative to one another.>siblings>parent-child>student-mentor>brothers in arms>lovers>vendor-customer>superior-inferior>friends >enemies>strangers
All of these can flow into one another, but some hold more dramatic potential than others.
And all of them can always very easily be made to flow towards lovers.
Because humans are strongly and on a basic emotional level motivated by sexuality.
Friendship holds little dramatic potential in itself. It is a bond of mutual affection, but relatively non-committal. They don't inherently have a defining cause, they don't have a fundamental imbalance of power or a shared fate that supercedes petty dispute.
It really is a fleeting thing and more an agreement of mutual convenience.
That's why you don't summon up a spirit of friendship in a team, but brotherhood.
Since capes are mostly not related by blood or part of a hierarchic organisation, they naturally gravitate towards lovers or enemies. Because that is where the drama happens. That is where high stakes and betrayal come in.
And with often unending need for twists and turns in the narrative, they gravitate towards the extreme ends sooner or later.
This is less pronounced if characters share a defined external purpose as brothers in arms. That purpose can generate drama, after all. Much more than just friendship.