There are multiple internal approaches to building things. Several of these approaches get funding and head count based on the amount of influence of the people who back them.

Decisions about which product to present to the public are made on technical merit with little consideration to consistency in user experience. The resulting chaos leaks to the end user.

Once a product has launched successfully, the best members (not just engineers) of the team that built it diffuses back into the main body of Google to work on other cool projects (they now have the required political momentum). Product enters stagnation phase.

In 2 - 4 years a technologically slightly better alternative is picked. No one thinks about how to make this switch seamless for their users. End users suffer even harder.

Used to work at Google.