The reality is that reliable backports of security fixes is expensive (partly because backports are hard in general). The older a distribution version is, generally the more work is required. To generalize somewhat, this work does not get done for free; someone has to pay for it.
People using Linux distributions have for years been in the fortunate position that companies with money were willing to fund a lot of painstaking work and then make the result available for free. One of the artifacts of this was free distributions with long support periods. My view is that this supply of corporate money is in the process of drying up, and with it will go that free long term support. This won’t be a pleasant process.
This is why I tend to use rolling releases. The only non-rolling distro I use is Fedora. For me, backporting security updates seems rife with issues due to questionable familiarity with the codebase. The people working on the distro have to backport fixes to 100’s or even 1000’s of packages, and there’s a higher likelihood that they’ll introduce additional bugs because of this reduced familiarity.