they can't expand because of the location. there are businesses and houses around and making the stadium bigger would infringe on those properties right

and although regular ticketholders are important, there is way more money in the luxury boxes and corporate sales which chelsea is really well-positioned to take advantage of. That is why arsenal is doing so well. and arsenal's average attendance for BPL matches is like 60,000+ which isn't sell-out but it is huge