Yup, it lacks the soot dispersants and anti-foaming package levels that a diesel oil requires.   And since most Suzuki bikes don't have flat tappet valve trains (our bike is a living antique in that aspect) it may be somewhat short on ZDDP levels as well.

A diesel oil will strip all the sludge & crap out of your bike's engine, cleaning it up in a few oil changes to a very internally clean state.

Someone mentioned this action up thread, but they had thought the oil was breaking down.  If it was Rotella Syn, it wasn't even getting broken in good yet at 2,000 miles but may have looked dirty from having scrubbed a bunch of the residual filth out of your engine.

Another bonus for no clutch? No oil shear?
Of course, oil shear, from gears, etc, but when using  no clutch, less?

Oil molecules don't shear.  The polymer viscosity index improvers shear.  These are tiny bits of plastic that change shape as the temperature of the oil changes.  They thicken a hot thin oil so it tests like a hot thick oil.  Under mechanical stress these plastic bits get broken (sheared) and no longer thicken the oil.  There is a range of quality and cost available in VIIs.  The best are extremely shear stable.  I looked at a product data sheet for a better oil than Shell Rotella T synthetic, and even this oil uses "a highly shear stable viscosity index improver."  Among the reasons this is a better oil than Rotella syn is that it is about 75% Group III base oil and about 25% Group IV (PAO) base oil.  I don't know if a wet clutch shears VIIs.  The transmission gears do shear the VIIs.

Shell makes the base oil in Rotella syn by refining crude oil.  It has the legal right to be marketed as a full synthetic in the U.S., but is not a "true" synthetic like the polyalphaolefin or the ester base oils.  Chevron has great web pages describing their Group III base oil and how it is refined from an intermediate product in crude refining, vacuum gas oil:
http://www.chevron.com/products/sitelets/baseoils/isodewax.aspx
And here's Chevron's description of the performance of Group III base oil...Chevron calls theirs Unconventional Base Oil, UCBO.  Shell calls theirs Extremely High Viscosity Index, XHVI.
http://www.chevron.com/products/sitelets/baseoils/grp3_perform.aspx

So, among so-called synthetic oils there are differences in the cost, performance, and chemistry in the base oils, and differences in the cost and performance in the additive packages including the viscosity index improvers.  Probably the best synthetic is PAO mixed with some ester base oil.  Group III with some PAO is excellent.  The best Group III base oils are very good, and there are some low cost Group III on the market that just meets spec and aren't that great.  Shell makes a very good Group III.

Here's a comparison of various base oils showing where PAO is better and where Group III is just as good:
http://www.chevron.com/products/sitelets/baseoils/comp_med.aspx
Conventional oils will be made from Group II or a base oil above the Group II spec but not quite Group III unofficially called Group II+.  A 15W-40 is probably a mixture of Group II and Group II+.  A conventional 10W-40 is probably Group II+ with ample VIIs or cheaper Group II with lots of VIIs.  Just about every oil, conventional and many synthetics will contain VIIs.  Less VIIs and higher cost/quality VIIs are better.

Viscosity index is a numerical index of the viscosity change in oil from 40°C to 100°C.  A higher VI number indicates an oil that thins less when hot and thickens less when cold.

Since I can watch the oil usage go up as the oil gets about 2,500 miles on it, I feel confident it is shearing, the shorter chains are more able to go into places & be burned off or leak out. So, I change it. The parts are well protected, I believe. I have learned the pattern & I change it as soon as I see an increased use.

Exactly.

Mobil 1 claims 5,000 miles for normal Mobil 1 and 15,000 miles for red cap "Extended".

Red cap "Extended" meets the Savage requirements for ZDDP.  So does Mobil 1 V-Twin motorcycle oil.   Note:  Mobil 1 normal car oil does not meet Savage ZDDP requirements.  

I could not see trying to run them for 15,000 miles any more than I could see shooting for 100,000 miles on a crankcase full of Rotella Synthetic.

We ain't got a car and we ain't got a 10 micron or better by-pass type oil cleaner like them diesel boys use.  Normal biker guys put about 5,000 miles a year on a bike, so synthetic oils should be good for a calender year for us,  IF ....

..... if you run a super magnet on your oil filter to get your metallic bits out of the oil

..... if you will always dump it and change it out if you have a fuel contamination issue

..... if you use enough oil to "top off" the oil occasionally to keep your additive packages refreshed.

So with m1 I can go 5k miles
currently change oil every other month, but in the heat of the summer it look like I burn a qt of RotSyn a week.

I will pick up a gal of m1 and see how long it lasts.