These are the reasons he wasn't interesting until 2006-2007.
During his early career, Rossi was a contrived media construct that Valentino consciously manipulated. He toyed with his opponents by under-utilizing his equipment and skill. He ran his opponents off the track. He spent more time planning his celebrations than training. He would put Saturday Night Specials on his bike for WUP, and then declare that he and Burgess had 'found some setting' by way of their superior experience and skill.
After the championship defeats in 2006 and 2007, Rossi dispensed with the ridiculous caricature, and he worked to improve his skills and race craft. He also quit toying with his opponents and he exerted his political power to mess with the GPC. At the 2009 Catalan GP, he managed to pass a Spaniard in the final turn without causing an international incident. I suggest that Rossi became a real person after 2006 and 2007. While his fans were busy trying to lynch Hayden, Stoner, and Michelin for proving that Rossi couldn't walk on water, Rossi was busy training.
The character Rossi played pre-2006 was devoid of substance; therefore, unworthy of attention.
