The growing concept of "IC" goes hand in hand with the increased focus on "leveling" for engineers, as well as the rise of delegating all product related decisions to the rising class of PMs. All of these create a structure in which every team, even across companies, starts to look more and more the same and any individual can be trivially swapped out for another with the same role and level.
In the early days of the startup boom, ~2008, engineers at startups had a lot more control over the product process. Typical startups where a CEO with some general vision of the product and a knowledge of fundraising and a technical cofounder who would handle the real implementation of the product. CEO would make sure the company was health, CTO/tech cofounder would make sure the product was built.
But this lead to a class of labor that was a bit too powerful. As you likely remember engineers used to contribute a lot more than purely churning through tickets.
Today you can think of IC as a prefix to a more complicated part number: IC-SRE-4, IC-DEVOPS-2, IC-DS-6. Then you just have to find someone claiming to be the part and send them through a leetcode grinder to verify the build quality, then plug them in and go!