Do you know the logic behind the uses of the two clefs? I don't see it. The switching seems rather arbitrary.
I'm not going to speak for Isaac, because he is a talkbass contributor (or was, at least), and he will hopefully chime in on his own arrangement. That's if he wants to take the time out of his full-time schedule playing the bass with the New York Philharmonic, to engage in bass talking with us.
Regardless, I'm glad that Isaac made this arrangement, because it shuts up the few students that I get who whine about tenor clef. (At least it gets them to shut up about tenor clef, and they might get back to playing the bass.)
One reason is that paper used to be expensive. Ledger lines use up more paper. More clefs can get rid of ledger lines. There's no good reason to use tenor clef any more, IMO. I've seen at least one piece for viola da gamba that used 4 different clefs.
I have noticed that living contemporary composers in general, are not writing new pieces in tenor clef for bass (solos or orchestra). So, they are one step ahead of you. As for the old standard stuff, unless someone makes good tenor-clef-less editions of the old solo warhorses, and the major orchestral publishers start making mistake-free orchestral parts that orchestras (and their librarians and their principals will adopt), we are stuck with tenor clef, even if the newer stuff coming out doesn't use it.
It's just tradition, and modern editors not having the courage to change it. I'm very tempted to produce modern editions of the standard repertoire (Koussevitsky, Bottessini, Dragonetti etc) in bass and trble clef only, but it's finding time! All of my adult class complain about having to learn 3 clefs, and it really is pretty pointless
We've all thought this at one time or another. And after many many decades, no one really makes an effort to make good new editions without tenor clef (with some notable exceptions like the Trapkus Koussevitzky), and you know why?
1) When anyone tries to make a tenor-clef-less version of standard solo bass repertoire, they find out that the ledger lines, 8va markings, and switches from bass<> clef introduce new problems that are just as onerous as tenor clef
2) we have better things to do, like play the bass, than make tenor-clef-less editions. Like you say, it's simply not worth the time
3) pointing out the obsolete-ness of tenor clef and so we should get rid of it is like saying we she should abandon pianos because they are not intuitive interfaces for music written after the Viennese common practice period (17th-18th century tonality)
4) but most importantly, tenor clef ain't rocket science, it ain't higher math, it ain't like writing new operating systems, it ain't like learning Mandarin. If someone puts in just a little bit of time & energy, students can become fluent in tenor clef. But first they need to shut up about tenor clef, and we as teachers need to stop enabling some students' tenor clef helplessness