The Chromium versioning system has more to do with how long they support a version of Chrome than anything else. It's much easier to say, "We currently support versions 96, 97, and 98 of Chrome than 5.5 build 4500, 5.5 build 4667, and 5.5 build 4800." This is simply because most people will only think about the version 5.5 part of those version numbers and completely miss the build numbers. Another useful thing is remote troubleshooting. I can easily tell someone, "Click the three-dot menu in the upper-right below the 'x', hover over 'Help' and select, 'About Google Chrome'. Read me the number next to the word 'Version'." If I hear 75 I know that a re-install of Chrome is in our future (and I can tune out them trying to parse the rest of the string) If they say something within a couple of versions (95 or above right now) I'll try to make it work.
By the way, while I pulled those build numbers out of thin air, they aren't too far off. My current Chrome Beta install says version 99.0.4844.35. It's quite likely that we'd see four-digit build numbers being the delimiter for the standard releases if Chrome tried to use something like semantic versioning.