The engineers that did that have gone, replaced by newer folks...

As companies get larger, the engineering talent reverts to the mean. The first crop of engineers, that were passionate about it, and made it a success. After they move on, they are replaced with average corp. employee, that joins Spotify as safe/boring job. Hence anything interesting gets removed, and the most boring features survive.

Ps. I was one of the involved on that feature. I didn't write it (It was done in Sweden), but I created one of the earlier demos, (and patents), and that eventually became touch to preview.

I'd love to see a linkedin scraper tool that 'visualizes' where the engineers go who originally worked on a product.

like here, where are those spotify engineers now... and how do the products they work on now, compare

This seems very plausible, as an outsider looking in. There's also the problem of when new people get hired and out in charge of new sections of the product, and they feel that they either need to make a change to justify their existence, or that they have found something that really works well for the way that they use the product without realizing the variety of ways that the user base uses the product.

It's already been happening I think. One of the core members of the team who built the music recommendation features left a few years ago https://notes.variogr.am/2016/11/16/leaving-spotify-the-echo...

Didn't they rewrite the client to share more code between the ballooning number of devices they're supporting?

But it increases three and a half key metrics, including engagement!