I can't blame people who have stopped playing KF2. I stopped too and I play rocket league instead...
This is just logical. At the beginning, there was hype. People buy, play it, and then wait. Now, the wait is longer than everyone was expecting.
With only 4 perks, and three maps, people get bored fast.
Five months latter, 2 news perks + berserkser overhaul, people come back, get bored and stop.
3 months latter; 1 new perk, Gunslinger (at least gunslinger was good from the start)
3 months latter : Nothing... No information regarding skill and weapon. Nothing (except : sharpshooter is the next and we will have LAR and crossbow).
So, basically, too much time between update makes people bored.
Also, some small fixes asked a long time ago are still not done.
Finally, even though we got 7 perks currently (same as KF1), because there is so little weapon for each perk, you don't have too much choice in loadout. In KF1, with 7 perks, you could have 14 different and viable load-out.