Cost, surely. Paying for 10 engineers is much cheaper than paying for them and the IP they helped produce over the years, especially if you're not interested in that IP.

Aquihires can be very destructive.

You end up with either the whole company, or you piss off the people that you wanted when you fire their co-workers. It also pulls in an almost complete graph of employees who are isolated from the new parent company.

Its much better to pull off the people that you want, and get them to join willingly, as they tend to adopt the culture/learn better when in isolation.

Cuts both ways. You also get a fully functioning, self-contained team or 10. That can be attractive.

Poaching can be done quietly and cheaply, acquihires get everyone publically.

I suspect this would work in a lot of cases if you can find out who the key engineers/strategy people in the company are. But working that out is probably the hard part.

If you have the money an acquihire guarantees you get everything. But then you still have to work out who those key people are after the fact and make sure you keep them happy.

Cisco poached all of the server sales team from HO when they launched UCS. This caused a major problem within Cisco because that HP sales team (and engineers) were so absolutely atrocious that it ruined Cisco internally for almost 10 years.

Aquihires are really only a thing when the target is a start-up with little revenue and limited growth prospects. At the time, Borland was a real company with many products and paying customers.

The majority of Borland products completed directly with Microsoft products at the time. If Microsoft had done an acquisition then they would have sunsetted most Borland products anyway so it would have been a pointless waste of money.

Buying a company to get 10 key employees is a lot more expensive than just making 10 really lucrative offers. For Microsoft in particular it left a competitor with a storied history rudderless. So it makes Microsoft's offering look even better in comparison.

If you approach people one at a time and make them personal offers that they accept, you can be pretty sure you end up with people who want to work for you and have at least some initial loyalty and desire to stay. If you acquihire then you end up with a lot of people who feel like they've been forced to work for you and will be looking for the quickest possible exit.