I think my loss of interest was more about discovering the entire tech tree, I don't think making things harder will be enough to draw me back. I know there are mods that add technologies, though, maybe those are worth trying.

Well, it sounds like you got plenty of value from the game so maybe moving on isn’t the worst thing. I love Factorio, but there’s so much out there demanding my time maybe it’s best that I also lost interest eventually.

Given the tech tree is infinite, that's impressive.

It's 'infinite' on a technicality. Having your last few technologies on repeat all so your investment in tech-making infrastructure doesn't completely go to waste just barely qualifies, nothing more.

It feels like the only reason they even left it in the game was that it became a bit of a measurement of how well your design scales past the end game - I cannot tell you how many otherwise meaningless 'X000 science per minute' base videos there are on YouTube, but the number is not insignificant. Most of the time it's just 'bot speed++' over and over again, since that's how many of those bases work without running into extreme update per minute (UPM) problems.

Infinite how? Seemed pretty finite to me.

There are some numerical upgrades which can be repeated indefinitely at increasing costs -- robot speed, mining productivity, damage for various weapon types, etc.

Pure angels alone is quite amazing. Especially if you enable the overhauls too. (Industries and technology)