At that time, Ubuntu would have been around for 14 years and it is increasingly getting more and more bloated. The same goes for many other distributions.
So, even if anyone wanted to run Ubuntu on an older machine, it would not be a good idea. Computing would have to be done at a rather glacial speed.
The idea of dropping the 32-bit build was first raised on the Ubuntu mailing lists in February by Bryan Quigley. Several other distributions like Fedora and openSUSE have already dropped their 32-bit images.
Of course, there will be some who grumble about this; Linux users are famous for grumbling about anything and everything.
But it is more than a decade since distributions started providing 64-bit images; I switched to 64-bit Debian back in 2003.
At that stage, there was no version of Flash for the platform and several applications had yet to catch up. But now, practically everything that is in common use is available in 64-bit so the disappearance of the 32-bit images should not pose a problem.
There are proprietary applications like Skype which are still available only as 32-bit for Linux, though Microsoft, the owner, provides 64-bit apps for its own platform.
Open source developers have no control over such proprietary apps – though I note that one enterprising person has made available an unofficial version of Skype for the Ubuntu Phone!
Given that there are more than 300 distributions, there will always be some distro or the other which can be run by those who like their 32-bit machines.
One of the great things about Linux is that there are plenty of choices, so one doesn't have to always run the Plasma or Gnome desktop environments which are both quite bulky and require robust hardware. Rat Poison, for example, is a minimalist environment which runs extremely well on older hardware.