Many of these RS tunes made the top twenty.  Perhaps they are 'obscure' because of the tunes' age. 

None the less, I think it would be hard to find a band, past or present, that has such a large catalog... hard driving rock, ballads, blues, psychedelic and probably other styles/genres I haven't thought of.  That in itself may justify an 'overweight' of RS song lessons.

Is the long run of RS song lessons eyebrow raising?  You bet.  But aside from what drives the business decisions of a private company, the publishing of such a long string of RS lessons should hardly be considered a negative.  Could other groups' songs be published?  You bet, assuming the bands/publishing houses permit such at an affordable price.  For at least a couple years that I know of, either musicians have repurchased the rights to their own music or, conversely, sold out their total catalogs to publishers.  How that affects GT gaining rights to produce lessons is an unknown.  It is a private company.

I imagine the stretch of RS songs will end... even their catalog is finite.  But the complaints/dissatisfaction (dis-Satisfaction... get it? 😉) will continue.  It wasn't long ago posts bemoaned the infrequency of song lessons.  Now, the complaints boil down to too many/too frequent lessons "I" don't like. 

Me?  There can never be enough lessons for songs from the first decade of R&R/Top 40, although I'd be content with the second decade as well.  That leaves the last five decades for the rest of youse guys to fight over.  Unless you wanna talk about Country/C&W, folk, a half-dozen Hispanic genres, R&B/soul/rap and hip hop and on and on and on.