Why doesn't having Xbox game pass ultimate give you another free username change?

Unfortunately the reasons for not allowing you to change your gamer tag still remain whether or not you have a subscription. There is issues of database stability and accountability

There are games for free on gold, why not give the Ultimate game pass a try, I have it, there are so many games, it is just great value

Live Gold: This is needed for Multiplayer games (that aren't free to play). However, only Ultimate Game Pass includes Live Gold..standard Game Pass doesn't include it. If you need Gold, then get Ultimate...normal Game Pass and a separate Live Gold sub would cost £15 a month (UK pounds, no clue on your local currency)....Ultimate (which includes both) is £10.99 a month

Games: If the game is on Game Pass, then it will be free to play it for as long as you have a Game Pass subscription. However, games sometimes leave Game Pass and would then become unavailable

However, Game Pass also gives you a discount for any Game Pass games that you then decide to buy.

Game Pass Ultimate also gives you access to PC Game Pass if you ever want to play games on a PC as well

This page covers everything, including an explanation of the differences between the 2 Xbox Game Pass Subs:

https://www.xbox.com/en-GB/xbox-game-pass

Is it Game Pass or Game Pass Ultimate that's overdue? Ultimate includes Gold which is why you would get that message when trying to add more Gold.

If it doesn't give you an option to pay the balance there, you'll need to contact support and speak to billing. You'll have to request a call or chat with support at http://support.xbox.com/contact-us
If you don't see those options, change your category/topic until you do.

Minecraft and Descenders are not free games. You can play them for free if you have Xbox Game Pass or Game Pass Ultimate. An Xbox Gold subscription allows you to play multiplayer games online but does not give you access to the games without purchasing them.