Why does Ubuntu need to reboot so often?

I guess you are referring to the latest update.

It included a package called linux-firmware which is a package that provides firmware used by the Linux kernel drivers so it was a kernel related update.

So to answer your question or better to correct that statement, Ubuntu doesn't need to be restarted on every update but just on updates which are related to kernel stuff.

I'm not sure of all the packages that require a reboot to finish the upgrade, but it is easy to find out why in specific cases.

The warning is triggered by a postinst script in the package. It creates the file /var/run/reboot-required The file /var/run/reboot-required.pkgs will list the packages that require the reboot.

It's worth saying that Linux also needs rebooted after other package updates too.

I'm a big Ubuntu fan but the frequency of package updates (because it's so bleeding edge) is far higher than other distributions.

The extent of which has meant I've dropped Ubuntu on some Servers in favour of Debian.

If anyone else can add to this list of packages that need a reboot it would be appreciated.

I use the superb checkrestart from debian-goodies (it uses lsof) to check when older libraries are still in use.

Updating these packages force a reboot:

Kernel packages (not all, like the meta packages) libc dbus

I'm only really concerned with Ubuntu Server and not the Desktop because only rebooting my Servers gives me a headache!