They didn't spend a decade working on it, they had an idea back in 2014 that they were thinking about in the finance department, nobody was writing any code for Genie or
Genie+ back in 2014.
Disney Genie and Genie+ is something that probably started development somewhere in 2018 or 2019. The screenshots you saw in 2019 were just concept art to demonstrate how it would work.
It doesn't take 10 years to develop a new fastpass replacement or even a system which recommends rides. It probably would have launched in 2020 if it were not for the pandemic. I'm sure Disney didn't want to launch it right around when the 50th started, it would be better to launch it before that and allow the software to become stable and the customers to simmer down a bit.
They didn't implement it years ago - because like the thread said back in 2014, Disney felt they didn't have enough 5 star attractions to charge money for it .. and like that person said, they had to wait until Toy Story Land, Galaxy's Edge, etc were completed first.
If Disney IT's track record is anything to go by - they don't want to develop anything from the ground up either - they re-used what they already had that worked which would be the MaxPass system - they've already had enough issues trying to integrate it into My Disney Experience & the new Park Pass system.
I think the Disney marketing has you thinking this is some revolutionary new system that will use advanced Machine Learning to figure out what
Lightning Lane passes to offer you.
We're all making assumptions here - but mine is that based on their past history it isn't something revolutionary or fancy - it is just going to be a simple system that now costs $15 to use. Even Disney Genie itself will probably utilize simple systems to look at park crowds and wait times to make recommendations - hopefully not to everyone and only a certain percentage of people.
We'll see soon just how advanced Genie is I guess.