Why would he spend money on a team that...
1) Is likely to be relegated within 13 games.
2) Outside of the transfer window so no chance to change thing.
3) Has huge debts of £60m+.
4) Has a small fanbase averaging a mere 18k in the top flight.
5) No training ground
6) A small and old stadium that also doesn't own the land around it.
There are plenty of Championship clubs with a lot more potential, infrastructure, larger fanbases and fewer problems than Pompey.
Sheff Utd
Sheff Weds
Derby
Leicester
Coventry
Newcastle
West Brom
Cardiff
Nottingham Forrest
Ipswich
Norwich
Leeds
Bristol City
Charlton
MK Dons
Middlesbrough
Are all clubs that a rich buyer should buy over Pompey.
Anyone that does buy Pompey can't be taken seriously as doing it to improve the club because the very fact that they choose Pompey over the many others they could have had shows a lack of business foresight.