If the total accumulation of year to year profits was higher than 1.8B, then the current owners of Stack Overflow would've never sold.

Maybe they wanted the cash in hand rather than a high variance company valuation. Or just wanted to transition their money and attention to something else. There are plenty of reasons to want to sell a company in a way that both sides come out ahead.

Also keep in mind that the public SO doesn't even have to change much for there to be "big changes". SO Jobs is where the money is made and they have private Q&A sites for businesses.

Perhaps they want liquidity, a more diverse portfolio, etc.

A bird in the hand is worth two in the bush.

If 1.8 billion in the hand is worth more than 1.8 billion year to year, then Prosus would've never bought.

The only way this deal is advantageous for both parties is if something changes, and unfortunately that something is probably Stack Overflow.

Or you can pump it, promise lots of new technology and "synergies" and profits and then dump it for a huge sum to VC or Big 10 company while it's still promising but you're pretty sure it's time to dump.

Which leaves bigger debt for users to overcome and work past to continue to see even the original value prior to all of this financial activity.

If the burden gets too big, people won't believe it's worth it, and the whole thing dies.

When they do a valuation of a company they also take into account future profits. So all of it should be included in the price.