Having worked on such large conglomerates it’s closer to friends & family discount than from large external company discount.
There’s also transfer pricing and other accounting ways to improve numbers.
This is so widespread that one such company had <company color> dollars (internal purchases) and green dollars (external customers) pricing.
Every major company operates the same way.
When Disney+ "buys" the right to stream the latest Marvel movie from Marvel Studios, the company as a whole has to back out the revenue so not to count it twice. But still show Disney+'s profit.
Disney+ buying from or selling to Marvel would not show up as profit or loss for Disney.
Making up numbers:
It costs Apple $800 to make a MacBook. It "sells" the MacBook to Apple Retail for $900 wholesale. Apple corporate now has revenue of $900 from the Mac it sold.
Apple Retail sells the same Mac to the end user for $1000. Apple Retail now has revenue of $1000.
Apple Corporate claims revenue of $900
Apple Retail claims revenue of $1000.
Apple claims a revenue of $1900. But it has to back out $900 of revenue so it doesn't double count it.
Apple wants to show that Apple Retail is profitable.
I used Apple instead of Disney in the example because it is much simpler to show one item being transferred from Apple to Apple retail than it is to show a group of movies being transferred to Disney and Disney selling a subscription.
That's on the user side, though. Like AWS and Azure, chances are GCP/Google's internal hardware division bills internal teams similarly to external customers (especially as Sundar continues to demand cost cuts). Of course users themselves can't go and make their own website and experience the same economies of scale that only big companies can achieve, but if competitors come in (like ByteDance) there's nothing stopping them from stealing marketshare from YouTube if they invest in some colocated servers in key markets.