Likewise "i18n" (internationalization/internationalisation) and "l10n" (localization/localisation) avoids confusion of whether it's "ize" or "ise", which is literally the problem those concepts try to solve.
I can somewhat excuse "k8s" with "nobody can remember how kubernetes is spelled let alone pronounced" (Germans insist pronouncing the "kuber" part the same way "kyber/cyber" is pronounced in other Greek loanwords, with a German "ü" umlaut) but I admit that one is a stretch and "visual puns" like "k0s" ("minimal", you see?) and "k3s" (the digit 3 looks like half of an 8 so it's "lightweight", right?) are a bit beyond the pale for me.
There are at least a dozen languages where the English word "accessibility" translates to the same word spelled slightly differently.
I'm not saying it's difficult to understand. I'm saying it's an unwieldy word and "a11y" is easier to remember and write correctly.
Also, "a11y" looks too much like the English word "ally". That, IMO, is more likely to cause reading difficulties, particularly with non-native speakers and people with dyslexia.