Question about Founder Role Post-Acquisition

My firm is a large business that has an investment/venture arm looking to acquire a smaller company, primarily for synergies with an existing portco and for its IP. For some reason my manager keeps insisting that the founder becomes an employee of our company post-acquisition, rather than stay as the head of his own company, even if his company becomes an operating subsidiary of the portco. Founder is also the one who built the company. Manager is not explaining the rationale / strategy behind this idea. Is there some risk for the founder to be head of the portco company that would be mitigated if he is an employee of our company?

Not seeing why founder would be an employee of our company post-acquisition, rather than lead his own / build another one in a different sector.

Would the rationale be something like: Google / Google Ventures acquires a company like Wavii, which was created by a sole founder. They seemingly acquired this primarily for its tech, IP and financial benefits etc. and then closes down the website and phone app, but continue to benefit from the Wavii IP/ technology in other internal divisions, which seems to be a fairly common acquisition play in the tech world.

Wavii founder then became part of the Google staff for 3 years post-acquisition. I'd imagine this may be some formality as part of a retention/non-compete agreement, but would there be some other rationale?