Thoughts:
1) Different things have different meaning and importance to different people. I think it is impolite to say to someone, "XP here does not matter, you should just ignore it and note care about it". It obviously natters to the OP, because the OP decided to post about it. It's not as though the OP was expecting to be able to buy BGA merch with the XP. The OP simply wanted to know why XP might decrease without explanation, and indicated that an explanation would be appreciated. Nothing unreasonable there. Maybe there could be an automated system message in the inbox.
2) Different people can have different opinions, but at times here on BGA, there is a sense of "ganging up" on one person in a thread who sems to have a minority opinion. Sometimes with minimal kindness or compassion or understanding, and sometimes with overt abrasiveness or condescension.
3) Sometimes, in these situations, assumptions are made based on very little. "If you're so bothered by this ...." or "You seem to only care because it happened to YOU", etc. People pounce on a possibly questionable word choice and then make all sorts of inferences or assumptions that are often completely off the mark.
4) I think the XP system is pretty cool

I like getting the achievements, having them pop up after a game when I wasn't expecting it, and gaining a high-value achievement. It's a neat reward, even if it doesn't "mean" anything. I think it's cool that there is a leaderboard and that someone has 8 million points. If that player awoke tomorrow and had only 4 million without explanation, would anyone tell that player, "who cares, they don't mean anything"?
5) Sometimes people who seem to have more programming knowledge and/or development experience talk to people in a way that is ... not conducive to making friends or generating polite and constructive conversation.
6) I myself may have been guilty of one or more things in the above list sometimes. Usually, it happens because I do not look over my reply and check whether my tone or word choice might be inadvertently conveying negativity that I am not intending.
7) Here is how I would have responded to the OP:
"I can understand how it would be frustrating to lose XP that you have earned. Here are some possible explanations, and some possible solutions. Most likely, BGA will not make any adjustment, but, it can't hurt to contact BGA support and ask. Best of luck

"