There's a delicate art in comforting the new members of the family that we're all in this together while systemically replacing their middle management with more suitable candidates.
And just because you're an 'exec' at an 'ok startup' doesn't mean you're generally qualified at that level. It's very hard to jump to another, similar job in the field.
Not saying it is right, but makes sense for a business of that scale.
The total market the acquired company could have penetrated never gets developed and fundamentally they decide to take an exit now for less risk and more cash early for what could have been a stronger contribution for the economy on the whole via a well-exploited niche.
A mundane example would be how the developers behind Firewatch were acqui-hired by Valve. They had a well-developed following and a hotly anticipated second product, an original single-player IP, somewhat rare nowadays. Half the team dissolved to work on Steam and the rest funneled themselves into Half-Life: Alyx. The new game was delisted from development.
These acquisitions are not 'big bangs' like VC investments where one will make the bank.
They are large and small investments across the board - some for know-how, some for talent, some for product, some for brand (ie Beats), some for code etc..
An acquisition is expensive beyond the price tag, especially in terms of opportunity cost if you bet on the buy and it fails.
M&A and cooltech is by far the easiest part. Making use of the tech, the talent, operational integration, re-writes vs. integration, product alignment, etc. it's very hard on every level.
What do you do with the VP of a 50 person company, now they are managers in a little team, the software might be discarded, or just a few ideas used from it etc. etc..