I don't think it's about difficulty -- it's about freedom. The movie reboot went back in time to the TOS era, and we already know the future of the Prime-Universe versions of those characters and their world. So anyone telling stories in that timeframe in the Prime Universe would be limited in what they could do with the characters, since they couldn't tell any stories that would conflict with the known future. Starting over again gives them the freedom to tell bigger and more daring stories, stories that can stand on their own and form a cohesive whole of their own.
The novels have done the same thing where possible in the Prime continuity -- doing series set after the end of the TV series so we have freedom to change the characters and situations, or doing spinoffs featuring original characters. That way we don't have to reset everything to the status quo at the end. I think most of us prefer having that freedom when it's feasible. But novels about the TOS cast in the 23rd century are more limited, more episodic, generally more formulaic. There's only so much you can do with characters whose future is already set.
So once the decision was made by the filmmakers to go back to the original, most familiar and most popular incarnation of Trek -- the adventures of Kirk, Spock, McCoy and the rest -- then the only option that would really give the filmmakers total creative freedom, as well as the opportunity to do the kind of big, worldshaking stories that modern movie blockbusters demand, was a continuity restart.