The issue is the very best portal players are highly sought by the blue bloods as well, with the competition in many cases being more acute than for HS players. Very good transfers are highly coveted for several reasons:
They have proven that they can play at the college level. Even very good HS recruits may take a year to adjust/be good college players
They fill a specific need in many cases.
They only take up a scholarship for a year or 2 in many cases. This is related to point 2. Doesn't disrupt your recruiting at the position or block other players you will bring into the program.
I don't think it's a matter of "Fran's ability to do well" in the portal. He has faults, but he has been very good at identifying good players, and many times identifying who will be good before others identify they will be good. There are numerous examples at Iowa of such players (Olaseni, White, Garza, Murray twins, etc.) Also others who Fran was in on early but then they exploded their profile and the blue bloods came calling (Tyler Ulis is one). But there is a limited supply of really good players in the portal, and the competition is fierce for them. It's not just a matter of saying "we want you" to a guy in the portal.
Objectively, if I were a talented big in the portal, Iowa would be extremely attractive. Fran has demonstrated his offense can let talented big players shine, see Garza, both Murrays. You would be paired with Kris Murray, which means you have another NBA-type talent on the floor with you. And you would have a path to playing time (at minimum 25 minutes per game). Yes, Rebraca is back, but any talented big is going to face far more fierce competition for PT at a blue blood than Rebraca.
Sorry for the long post, but if, big if, Iowa can land the Utah Valley kid or the Stanford big or one that we aren't aware of, the team next year could be quite good/interesting. My opinion is that Bowen is going to be the best pure PG has had since Dev Marble. Bohannon was tremendous in his own way, but Bowen appears to be able to get in the lane, but also have a more well-rounded offensive game than Iowa has seen at the position in some time. Still has to do it, but Bowen and Perkins playing together is very interesting. Two guards with some size, who can both drive, pass and score.