Because he fought Tom Erikson in K-1 who's neither a boxer or kickboxer.
If anything bring up Botha beating Aerts and JLB and giving Bonjasky everything he could handle under K-1 rules.
Spreading rumours without any knowledge seems to be popular these days. Botha did neither beat Aerts nor JLB. Both of them injured themselves during the fight.
It would have been very surprising indeed if Botha actually would have defeated them because he lost against "Cans" far below their level.
Below are Botha's fights in K-1 between 2003 and 2006 that I know off:
20-05-2006 Jorgen Kruth L 3R Decision 3-0 K-1 K-1 Scandinavia Grand Prix 2006 in Stockholm
05-03-2006 Ray Sefo L 3R Decision 3-0 (30-27, 30-27, 30-28) K-1 K-1 World Grand Prix 2006 in Auckland
23-09-2005 Musashi L 3R Decision 0-3 (30-29, 30-27, 30-29) K-1 K-1 World Grand Prix 2005 in Osaka
13-08-2005 Mighty Mo L 1R 1:20 TKO (Referee Stoppage, 3 Knockdowns) K-1 K-1 World Grand Prix 2005 in Las Vegas II
04-12-2004 Remy Bonjasky L 3R Decision 0-3 (25.5-27.5, 27.5-28.5, 27.5-28.5) K-1 K-1 WORLD GRAND PRIX 2004 FINAL
04-12-2004 Peter Aerts W 1R 1:13 KO (Leg Injury) K-1 K-1 WORLD GRAND PRIX 2004 FINAL
25-09-2004 Jerome Le Banner W 3R Decision 0-1 (29-29, 28-29, 28-28)
-> Ext.R (Le Banners Corner throws in the towel)
-> 3R 3:00 TKO (Corner Stoppage) K-1 K-1 World Grand Prix 2004 in Tokyo
06-06-2004 Remy Bonjasky L 3R Decision 3-0 K-1 K-1 World Grand Prix 2004 in Nagoya
27-03-2004 Aziz Khattou L 3R Decision 0-2 K-1 K-1 World Grand Prix 2004 in Saitama
31-12-2003 Yusuke Fujimoto L 3R Decision 0-3 K-1 K-1 PREMIUM 2003 Dynamite!!
06-12-2003 Cyril Abidi L 3R Decision 3-0 K-1 K-1 WORLD GRAND PRIX 2003 FINAL
11-10-2003 Cyril Abidi L 1R Foul K-1 K-1 World Grand Prix 2003 in Osaka
That's 2 wins out of 12 fights and both wins were due to injury of the opponent. That can hardly be called a succesfull career.
Maybe you should talk about the whole picture and not only post those tiny tidbits that support your own argument.