Google would be in a better position to avoid losing important security features, falling behind on security updates and missing a major Android release for their latest Pixel generation if they hadn't done so many layoffs, buyouts and hadn't ended remote work. Ending remote work combined with offering people buyouts lost many of their best engineers and created the current ongoing crisis for Android and Pixels.
How could that be when previous models have it? In terms of timeline, it seems quicker not to remove a feature than to remove and test the new changes
There are leaked documents showing Google planned to remove MTE support from their custom CPU cores. If they planned to ship those with the Pixel 11, then using standard ARM cores with MTE support was a change of plans. They should have been able to get MTE shipped but they've laid off so many people recently.