That's because those routes havent changed.
If a route gets too congested, it sends messages downstream telling routers to stop sending it data, because it cant deliver messages. This is how the internet
"Routes around damage" (Tim Berners Lee, one of the fathers of the modern internet, has famously asserted that attempts at internet censorship by totalitarian regimes, and efforts like traffic shaping, will ultimately trigger this mechanism, and the internet will simply route around the "Damage".) If it does not receive messages from the upstream host for acknowledgement (ACK), it also triggers this mechanism, and the route gets pruned. This is how the internet deals with things like severed undersea cables, or with cities getting blown up, like in the middle east. This happens automatically without any net admin's intervention.
Because the network is dynamically reconfiguring, and choosing outbound routes based on availability and router-to-router communications, the routes can and do change spurriously based on use, as long as a less congested or higher availability route is available. If you have a shittily overcrowded link between your ISP and one of it's
peered networks, then the currently favored route for a given destination could constantly be changing, which can be confusing to your crappy home-grade router.
I have similar problems with the DSL modem I am forced to use. Thing's horrible. Needs rebooting at least once a month. Total trash.