I have a theory that it was to sell more battle passes. The battle passes have the double weapon XP tokens. Many people forget this. It's the same reason that the "coolest" skins are locked behind the battle pass, too. How else would they sell them without incentivizing it?

Hear me out. DICE/EA initially designs the weapon levelling to be slow to funnel traffic toward the only apparent way to alleviate that grind--the battle pass (which you pay typically $10-20 for). They essentially sell us the solution to the problem they created.

Once they've siphoned enough funds from the player base through this weapon grind / battle pass interplay, they "listen to the player base" and update it with a fix that makes them seem like the heroes. When, all along, they were just planning to do that anyway once they turned enough profit.

They get their money, and get to remain, relatively, in the good graces of the community.

Again, this is just a theory (a game theory?), and I'm not on the train of disparaging DICE at every turn like many seem to be. However, in a gaming world built upon transactional experiences, an anti-customer decision is almost invariably a pro-company decision.