Because Bruno is a better fighter than Rahman, plain and simple. Better boxer,, better puncher. Bruno only lost to high level fighters. Prime Rahman was knocked out by the awful Oleg Maskaev twice, and struggled with guys like Obed Sullivan for Christ's sake. Bruno gave a prime Tyson a reasonable fight for five rounds. Rahman would get blasted out by prime Tyson in 1 round. If you take away the fluke win over an overconfident and underprepared Lewis, Rahman has virtually no resume. And, in the immediate rematch he was decimated. Rahman holds no advantages over Bruno, including chin.
I also think Bruno is underrated in the power department too. When we talk about the big hitters of boxing we usually mention names like Foreman, Shavers, Louis, Liston, Tyson, etc.. but people seem to forget that Frank got 38 of his 40 wins by knockout. Even the guys who beat him say he hit extremely hard
Bruno had A level power A bunch of 80s/90s guys had serious power like Smith, Witherspoon, Bruno, Ruddock... These guys are in the same class as Lewis, Tyson, Foreman, Shavers, Wlad in terms of power
This is a fight against a ranked fighter / champion that Bruno can actually win. I'd give Bruno a slight edge here. Rahman was almost as basic as McCall and without the iron chin.
No Rahman was not that good. But he was still a clear level above Bruno, who feasted C level opposition, and almost invariably lost when he stepped up.
The problem is that Bruno basically always lost to high level fighters, while Ramhan won some and lost some against them. There is absolutely no reason to think that Bruno is better, except that he had bigger biceps.
That simply is not true. Bruno decimated several fighters that were on the level of or better than Rahman (Coetzee, Carl Williams, Jesse Ferguson, James Tillis). He bombed out Tillis around the time Tillis went the distance with Tyson. And, he destroyed Ferguson a few years before an old Ferguson took a basically prime Rahman the difference. As others have mentioned, Rahman was every bit as basic as the McCall that Bruno beat, but with a less than stellar chin.
None of those guys was a force at world level when Bruno beat them. Bruno never risked fighting anybody world class, unless there was a belt on the line, and when he did he almost invariably lost. McCall was Bruno's only major win at world level, and there is strong evidence that eh was already being impact by substance addiction. You may be too young to remember it, but Bruno was seen as being something of a national joke in the UK. A likeable loser, who always lost the big ones. Whatever you think of Rahman, his resume has very real substance to it.
Other than the win against Lewis - a well-documented anomaly, which was emphatically remedied, what is this "very real substance" to Rahman's ledger, of which you write?
Rahman has one elite level victory ... And that was against an unfocused, undertrained Lennox Lewis Yes better than anything Bruno did but Bruno actually gave Lewis more problems when they fought ... But Lewis didn't take Bruno as lightly and he trained to beat him ... Replace Bruno with Rahman that night Lewis was KOed and I have no doubt in my mind that Bruno could have gotten Lewis out of there with one punch as well ...
I would say that is a pretty good start wouldn't you? He also went on to reclaim the WBC title, to become a one time lineal champion, and two time champion. That is already putting clear blue water between him and Bruno. On top of that he had some other good wins, and draws.