Because people don't want to abandon hundreds or thousands of years of culture for a completely solvable problem.

I looked at Arabizi and the numbers are really annoying for formal text etc. Finglish is better in my opinion, however it causes problems like being able to read the same text in two ways. like "dar". The a can be like 'a' in 'dad' or it can be 'a' like in 'car'. with different pronunciation it means 'door' and 'gallow' which can be very annoying in Arabic languages that unlike Persian write _ُ_ِ_ٌ_ً_ٍ_ّ_. Instead of numbers it uses combinations like 'kh' for 'خ', 'gh' for 'ق' and 'غ'. In some methods they use 'aa' for 'a' sound like 'bar' and single 'a' for 'a' sound like 'lad'.

I don’t know either, but I am aware that in glyph based languages (and this article makes the case that Arabic has some glyph-like features), there is considerable social discussion about the equivalents, like pinyin. Detractors worry that sound-based (where sounds are based on the latin / western orthography) approaches to writing change something fundamental in people’s brains as distinct from more native versions.

In Chinese for instance, you can use a keyboard that combines radicals - parts of a character, or you can use a keyboard that combines phonemes. Those seem likely to change literally how you think in your language. There may be related concerns for Arabic.

That said, one of the complaints in the blog is that two different codepoints render to the same exact letter / phrase / word — this is not a problem unique to Arabic in Unicode, and there are known approaches: I’d expect (I’m not a Unicode expert by any means) that more work on the tech stack for rectification (I’m sure there’s a technical Unicode word for this process of matching codepoints for e.g. search and uniqueness of rendering) would likely be useful for Arabic, and relatively seamlessly flow in many places.

Probably because it's a work around and not what most people want to do. Imagine someone telling you you have to type English in Cyrillic. I know if I could no longer type out Chinese characters and had to use pinyin it would feel very odd and like something was taken away.

For a while, Arabizi was wildly popular and universally used on feature phones. When mobiles became smarter, it was used less. Japanese has romaji and Mandarin has pinyin. Arabic's Arabizi would increase literacy rates and solve all these digital problems.

It's aesthetically revolting and allows for multiple renderings of the same word.