Why has google not put google ads on youtube yet? they are still serving ads from another company, when adsense offers exactly the same format. this seems silly, as google is losing money here.

YouTube probably has ad contracts with other companies that won't expire for some time. (Maybe the contracts say something like, "YouTube will not advertise the 'acquiring' company's ads for X amount of time in the case of an acquisition/merger/etc.") When these contracts expire, Google could put up its own ads.

If Google advertises its ads on YouTube right after the acquisition, it's not fair for the companies who advertise there now. They don't get "full exposure" – i.e. they don't get what they paid for if they have to compete with other ads.

I saw a few AdSense on YouTube the day of the acquisition... They are there, just rare.

Well they dont even fully own YouTube until the end of the year, so you cant blame them.