Greg, because Ahrefs is amazing for keyword research just as good as SemRush. You want to find more content ideas with Ahrefs. You can find thousands of keywords for many niches.
At Semrush you have much much more possibilities than on Ahrefs, when it coming about keywords data.
Because you are able to find very simple keywords for the moment where any site started growing for the last 7 years.
For next example, you can find great keywords + ad title/desc for Adwords, where by "great" I mean good CPM + conversions.
But Semrush same as Ahrefs or Moz, don't have TTF TF - which is necessary to increase SEO effectivity.
And this is why Majestic is the tool which any SEO professional "must have".
Also I would like to clarify, that at any time when I write the "beginner" - I don't have on mind any worse person.
I have on mind just small point on the experience road.
Because years back, I was also the beginner, same as everyone who have years of experience behind self.
And still I am the beginner for example in marketing area.
Because no one is able to be a guru in each industry at the same time.
Cheers, Greg.