The main reason would be fracturing people who would be interested in joining across different communities - someone might find a few LGBT+ communities and miss others, same as if someone made another LGBT+ community here on lemmy.world which some people join instead of yours. Activity, content and visibility in these early days of Lemmy are kinda tough to get, and spreading out across instances makes it tougher.
But, of course you're totally free to make your own community too! That's part what makes federation so cool, if you're unhappy with existing communities and/or their moderation you can always make your own, and people from anywhere else can join. Best of luck :)
'Subscribed' is called 'Frontpage' in the app, you can find it in the sidebar.