You didn’t notice, OK. I think new drivers are announced in due time in the update announcement threads. //EDIT: see two minutes later, Stable update announcement, and 455 drivers announced to the people [Stable Update] 2020-10-19 - Kernels, Nvidia 455, Browsers, 
Also 455 is not an update to 450. As you wrote, so you know it, this is another branch of the driver, and you can select the driver branch you want and each driver branch receive different updates. So I don’t see a problem with the current way it works. As suggested there are the metapackages for you if you want to have the “latest everything”, but some people don’t want to automatically switch driver branches every time a new one is out. That would be better for you, probably not for everyone.
//EDIT: actually no, linux-latest-nvidia-XXX metapackages are versioned so it wouldn’t help here for you to stay always on the latest nvidia driver available. Maybe a new metapackage could be created just called linux-latest-nvidia, the same as for the kernels.