Most houses are old and many in shit condition, you'd want at least replace shingles before installing solar.

Everything becomes harder and expensive - no more standard gutter cleaning fee (200-300 bucks per average roof). For damp subclimates no more moss treatment possible.

For many houses you'd need structural engineer assessment to make sure roof can add such a load.

Many vents and outlets need to be relocated to cover large and nice area with the panels.

Dealing with contractors on standard things is such a pain already in US - expensive, many unskilled, trying to get more money out of your pocket. When they see someting expensive or non-standard their attitude changes even more.