Collectively, google believes they are right and the world is wrong. Anything pre-existing is dirty and unworthy of their genius if they didn't invent it themselves.
Someone a bit more objective might say "Google believes that it's quite hard to integrate third-party software into their huge existing infrastructure and make it work at their enormous scale."
They might also say "Google believes the infrastructure they use is the right choice for their business needs, and Googlers like to tell the world about some of it, in case it's the right choice for them, too."
But I'm a Googler and you clearly have an axe to grind, so it's unlikely we're going to agree.
I used to work at a place that tried to reinvent everything from the wheel up, too. Over time I came to realize that avoiding third party libraries and technology stacks was more about long term support and hackability than anything else.
Unfortunately, newer recruits never realize this and accept the internal stack as religion. They never bother to learn third party alternatives.
We had a joke that went: "If you were ever fired and had to find a job elsewhere, you'll have to start by implementing your own X", X being a heavily used internal library that allowed an entire generation of developers to do certain things without ever knowing the underlying system calls.
Someone a bit more objective might say "Google believes that it's quite hard to integrate third-party software into their huge existing infrastructure and make it work at their enormous scale."
They might also say "Google believes the infrastructure they use is the right choice for their business needs, and Googlers like to tell the world about some of it, in case it's the right choice for them, too."
But I'm a Googler and you clearly have an axe to grind, so it's unlikely we're going to agree.