What is the reason the CTO can't join fulltime? I understand the investors thoughts that the CTO doesn't want to contribute fulltime, thus slowing the company

What is the reason the CTO can't join fulltime? I understand the investors thoughts that the CTO doesn't want to contribute fulltime, thus slowing the company down. CTO should be either replaced or joining fulltime. If CTO can't join fulltime for whatever reason he shouldn't be CTO but hold a lower position for which he could be paid part-time.