Google won the search engine market because it was objectively better and thus spread through word of mouth. The first time I saw Google run actual ads was when they pushed Chrome hard.

Facebook also spread mostly through word of mouth and only started doing ads when its public image deteriorated.

(Side-note: I'm in Germany, so this is about German ad campaigns. Also I have had adblockers for a long time, so when I say "they run ads", I mostly mean TV, print and billboards.)

You just described two companies that became the ad channels, so they certainly are a bit of an exception. Even Apple, who has the most word-of-mouth viral product line in all history, used advertisements from the beginning.

Tesla technically.

Tesla might not have advertisements on TV or radio, but it is not a coincidence that luxury malls have prime parking dedicated to Tesla chargers, that they have prominent show rooms and that their CEO is always getting in the news.