Most rebuilds are not about looks. They happen because the site was never structured to be found, could not be edited, or quietly dropped leads. All three are avoidable up front.
Most website rebuilds happen because the original site was never structured to be found, not because it stopped looking good. A site that brings in work rarely gets replaced, however dated it looks. The rebuild conversation almost always starts with a business owner saying the site does not do anything, and that is a structural problem that was baked in on day one.
It was built as one page pretending to be a business
Sites built as a single scrolling page with every service in one section cannot rank for any of those services individually, and that is the most common reason a rebuild becomes necessary. Google needs a page it can point at for each thing you sell. A section heading is not a page, and no amount of later optimization fixes it without restructuring.
Nobody could change anything
The second most common cause is a site that requires a call to the developer to change a phone number, which means it slowly drifts out of date until it embarrasses you. Hours go stale, prices go stale, and the photos stay from the year it launched. A site nobody can maintain is a site that expires on a schedule.
Leads were landing nowhere
Plenty of sites are replaced because the owner assumed nobody was contacting them, when in fact the form was sending to an address nobody checked or was silently failing. This is worth testing on your current site today. Fill in your own form from your phone and see what happens, and how long it takes anyone to notice.
It was rented, not owned
Some rebuilds are forced rather than chosen, because the business wanted to leave a provider and discovered the site could not come with them. That is a rebuild you pay for twice, once to build it and once to build it again. Confirming ownership before the first build is the cheapest insurance in this entire category.
Speed quietly ate the traffic
A site that got heavier every year until it took five seconds to load on a phone will lose both visitors and rankings without any obvious moment of failure. Performance decays as plugins, tracking scripts, and oversized images accumulate. It is worth measuring once a year rather than discovering it during a rebuild.
How to not be here in two years
Build it with a page per service, in something you can edit, on hosting you control, with a tested lead path and a mobile speed check once a year. That list is short and it is most of the reason a site lasts. It is also cheaper to do at the start than to do again, which is the actual argument for getting the first build right.