Update:
The community update released today states that the XP required to upgrade weapon attachments for the first 20 attachment ranks will be reduced.
However, if you take a quick look at your most commonly used weapons, you'll find that most useful/better attachments are after level 25, so I think the overall experience requirement should be reduced, not just in the first 20 ranks. Or the list of weapon attachments should be adjusted to put more useful attachments in the first 20 levels.
Battlefield 6 - Community Update - Player Progression and Portal Servers
