You're confusing software engineering with corporate product support. You can have top-notch ongoing lifetimes for trash products. See for example SAP or anything Oracle.
Product support is an integral part of enterprise software engineering.
Product management does not know what adding a new feature or deprecating an old feature means. It is the responsibility of engineering to provide the dependency matrix.
For example, engineering usually tells product, if you change feature A, then it will also affect feature B, C and Z. Otherwise you may end up with contract breaches and SLA violations.
Product lifetime and providing incremental features is a big reason why SAP and Oracle have been successful in the enterprise space and people still pay a lot of money to buy them.
People outside Google don't have the benefit of thinking of any particular project as being run only by the individuals currently working on it—those particular people may leave the company or change teams or move on to other projects. It's Google that's making it, and Google who will run it in the future, and we have to account for what Google might do with it 5, 10, 20 years from now.
No amount of the original Chrome team being excellent, well-intentioned, skilled, thoughtful makers can stop today's Chrome from cornering the market into an effective monopoly and leveraging that to try and benefit Google's ad products. That's one of the things you have to pay for when working for a large company—the support and knowledge and compensation are great boons but you don't get to just be yourself anymore, you're _Google_, your own work is always at risk of getting co-opted by others, and external people will view and criticize your work accordingly.