Every large space can be trimmed down to a small space. If there are too many vacant shops in an area, and there would be a market for smaller shops, I would assume that tenants add walls and rent out the smaller space. Even if that walled-off space is unused, tenants would make more money than not renting out at all.
The oft-cited counterexample to US restrictive zoning, Japan's permissive zoning, works because in Japan zoning type is decided at the national level and there are only 12 types of zoning that define maximum nuisance (so a blacklist). US zoning gets extremely nitty-gritty and is functionally a whitelist.
You can't just throw up some false walls and call it a day. Even if you could, your landlord's lease terms probably don't let you sublease like that.