I would put it down to 4 things:

- the internet's a lot bigger nowadays

- there are a lot of crappily secured iot devices

- the average household internet connection has gotten a lot faster, especially on upload bandwidth.

- there's a pile of amplification techniques which can multiply the bandwidth of an attack by using poorly-configured services.

Search for “residential proxy”.

This seems like a synonym for botnet.

Also a good synonym for "anonymized and deceiving army of AI crawlers circumventing controls for their own benefit".