Read the basics, stopped after a while. The big difference between google etc, and bugs on steam is that Valve can repair all the damage done on steam for low-little cost, while exploits on google etc, can cause real money damage, or situations such as forcing links/ads that are offensive/18+ to display for everyone, which is a PR disaster and hurts their security image since people tend to use google for email etc.
Also a lot of your points are out of date/wrong.
1: Makes a maphacking tool (just because everything happens serverside does not mean you cant somehow access that data. Maphacks are super profitable.
Making it server side means its impossible to make a maphack, that's why they did it, and why all games try to make it serverside if possible. You can only see SOME stuff such as techie mine locations etc, with the hacks that are possible, and they are very limited in scope.
2-4 Wipes your in-game inventory clean (goodbye dragonclaw hooks and anything else of value)
Scams your friends if they get control of the social features of your account for long enough to keep the gravy train going.
Uses you as a mule to launder money/items stolen from other users possibly getting your account banned in the process (esp if there is a chargeback, because you claim you didn't buy this or traded that).
All of these are out of date. All newly purchased items have a 3 month restriction from the store, and 1 week from trades/marketplace. This means, in order to steal your information they would have to get your info, have access to your data for over a week without you noticing, and THEN trade it to an account, wait ANOTHER WEEK and then try to sell everything for real $$ etc before being banned by Valve. To get stuff from your friends it would take an additional week, and your friends would have to be stupid to fall for it. As for using your account to sell, no one does that because the chances of a high value account not being used for over a week is ridiculously small, and you leave a much easier trail to follow since you can see who you traded with, and then tell them to do a chargeback since it was stolen, as well as getting the payment information.
Now the main reason none of these will work anymore, is because Valve added Email confirmation for all trade offers, which means they would now need your steam info, and your email info to actually make a trade, and since I dont think its possible to make a bot that can do manual trades (correct me if im wrong), its shut down scamming pretty hard in the past month.