What's the (economical) advantage for a company by paying an employee severance payment short before retirement
If Bob is actually a valuable employee this probably doesn't make sense.
However it is possible that the things Bob is good at just don't have a market any more. So his work could be good but it is not valuable (any more). Training his to do new things is not considered worthwhile with his upcoming retirement.
If he continues to work he probably also needs an office or similar amenities that are not needed if he is let go.
So one could construct examples where it is worthwhile to pay him his full salary until retirement as severance pay but it wouldn't be a typical situation.