* many new homes use metal "structured cabling" boxes (which block wifi signals)
* the box is not in a central location (eg: usually in a corner of the basement near where cabling comes in)
* Most people use their ISP-provided combination wifi/router
* The wifi is then located inside the metal structured cabling box
For most non-techie houses, if the access point is centrally located, it'll solve the vast majority of problems. However, to do this, practically, at least some of the following have to happen:
* The router and wifi need to be separate units, with ethernet cables to the wifi location
* The structured cabling box needs to be redesigned to be plastic or mount the router/wifi combo externally
* All the in-house ethernet and outside connections need to be run to a location near the center of the house, such that there are minimal walls between it and each living space
This isn't hard, it's just an incentives problem. Most houses don't sell for more money by doing this, so the builder has no incentive to fix it. ISPs have clearly decided that having a single modem/router/wifi combo is most cost-effective for them, and just let their customers deal with a less-than-optimal experience. In many cases people have little or no other ISP choice, so it's not like they lose the business.