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According to this Stack Exchange post from last year a full IPv4 routing table requires on the order of a few hundred MBs of RAM. This is indeed a tiny fraction of the cost of maintaining the global internet infrastructure.

https://networkengineering.stackexchange.com/questions/76562...

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The problem is that the routers that have to hold the routing table can only handle a limited number of routes. There is a good article from APNIC about the topic.

https://blog.apnic.net/2021/03/03/what-will-happen-when-the-...

Said routers could be redesigned...

And besides, there is no need to keep the whole routing table in RAM. Instead all that's necessary is a single integer per route representing which port packets to each route needs to be sent down. So even for a large router with 64 ports, the whole routing table fits inside 1 megabyte.

Sure they can create routers with more space for the routing table but you still have to replace all the old ones which isn't cheap.

A single port of a router at an internet exchange can reach more than 1000 different routers. A router has to decide to which IP it should forward a packet not just the port.

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