The really impressive thing about Valve is the amount of revenue they make with a relatively small head count. They have about 1/10 the number of employees as EA.
Seems about right. They don't have a complete monopoly and the industry seems to be making most of their money off micro-transactions these days instead of sales, something valve takes no cut of outside there own games. Meanwhile apple and google do have monopolies and take a cut of micro-transactions which accounts for there significantly larger revenue.
That number is shockingly low due to how prevent they are. They don't really have any competition on the PC market aside from the Epic Games store which is only used for exclusives by most.
But how could Valve have made $6.5b off of their own games? They haven't released anything in yonks have they?! Plus EA have the gacha-fication of FIFA/every other sports game franchise they own with Ultimate Team, etc.