You're talking about BF4? On PS4 at least there's still a ton of people playing both the OG maps and the DLC.
In fact I'd argue that it's partly thanks to the season pass that BF4 remained interesting for so long. We got 15+ maps over a year. With games that rely on F2P mechanics the drip of new maps is so much slower. Just look at Siege.
Mappacks are free now every other week. So thats why its probably more busy then normal.