I tend to believe and have witnessed, that most ABs regress and behave akin to their given genders, i.e. a male AB will have a preference for boyish behaviour and boy accessories and a female AB will have a preference for girly behaviour and girl accessories... Now of course, there are exceptions to the rule like Sissies and Tomboys for example
As far as whether or not the act of regressing is masculine or feminine, I'm not entirely sure
I have seen some people who treat AB time as a more relaxed, nurturing and I suppose you could say "feminine" act/pastime, but there are ABs who enjoy splashing in puddles, crawling around and exploring, very you could say "masculine" behaviours. In the end, I think this is something that is difficult to quantify, every AB/Little comes at this differently, it is personal preference and opinion that determines what an AB, male or female, is going to gravitate towards and how they are going to view regression time
Quite honestly, I find regression time and what I do as an AB to be fairly androgynous or gender neutral, I may identify as a true-blue AB Boy and have a preference for boyish outfits, but at the end of the day, the tenets of baby care don't discriminate based on gender; we all want a caregiver, we all need changes, we all love cuddles, so on and so forth
As for the 2nd note, I wholeheartedly agree, while regressing in and of itself is not necessarily more feminine than masculine or vice versa, as an AB who is male and regresses as a baby boy, I can definitely say that there is an abundance of female AB related items and accessories. An AB girl has a wider variety of clothing options for instance, AB boys usually have to make good with a onesie... I seldom see boyish shortalls, rompers and footies that are readily available
To put things in perspective further, Sissies who I would say make up a minority of Male ABs have more clothes and accessories that cater to their needs than a straightforward AB Boy does (I'm not knocking on Sissies, I know quite a few, I'm just saying they get these really elaborate, babyish dresses... AB Boy clothing is nowhere near as cute or elaborate as what Sissies get
). This has always seemed counterintuitive to me, if the majority of ABs are male and not all of them are Sissies, why isn't there more AB boy clothing and accessories readily available? I mean, there are AB Girls who deserve access to clothing and accessories that fit their AB/Little identity and I certainly don't subscribe to the old notions that the community is 80% male to 20% female, personally from what I've observed it's probably closer to 60/40, but still, that would suggest that AB Boy related content and merchandise would slightly outweigh female AB content and merchandise and it simply doesn't.
I don't know if anyone has the right answer as to why there exists more female directed AB accessories, clothing and content than male directed AB accessories, clothing and content. The nearest I can figure is that, as Kratox said, girls/women have a little more liberty and leeway to enjoy childish things. For instance, no one would bat an eye at a girl having stuffed animals or childish clothing lying around, but enter a guy's bachelor pad and see a row of stuffies lining his bed, some cartoons playing on the TV and some childish Ts and overalls in the closet, some people are gonna think that guys a wuss and possibly even tease and torment them. Maybe this leeway has spiralled off into women being more up front about AB/DL and DDLG? I don't know if that's the case, but I can see men being a little more reserved when it comes to this side of themselves... perhaps that's why there seems to be a bigger market for female ABs, maybe they are a little more outspoken and as a result, they have a bigger market presence? Maybe there's a chance some of these female related AB/DL or DDLG accessories would appeal just as well to women who aren't affiliated in any way with AB/DL or DDLG and hence, more sales? Once again, I don't have the answers, but its fun to speculate