I also wondered about this, so I googled "diaper bag". Literally all the results just look like normal bags. They aren't covered in rainbows and butterflies. Just a random color + bag.

Plenty of diaper bags with sportsball branding and Comic Books for Adults aesthetics.

Of course, there's a lot of military advertising in both of these media circuits, so... shrug Any time you need to make your diaper bag look like something other than a diaper bag in order to feel secure, you've been cowed by The Patriarchy.