The 11lb limit comes from the FAI limit for pattern of 2x2M max size & 5Kg max weight

Quite a few years ago there was also a 10cc (60) engine limit. There were calls at the time to have an unrestricted engine capacity limit to lower the cost of pattern as the 10cc engines were becoming quite specialised for pattern & therefore
expensive. If the engine size was unrestricted then cheaper but higher capacity engines could be used. Well engine capacity did become unrestricted, so did that lower the cost ? - NO it had the opposite effect and we got larger capacity
Specialised F3A engines that were even more expensive !!

IMO if the weight limit were increased then a similar effect would occur and cost would increase - I can imagine, for example, if a weight limit of 6Kg (13.2 lb) was allowed then we could get super “bloated” BiPlanes with full 2M wingspans and exotic/super expensive power systems to drag them around the sky....

Steve