bloop tubes
As to answering why a manufacturer makes a specific product ..that can only be truthfully answered by the manufacturer.
I can GUESS...and that would be that people are asking for the tube to be included on the tuner - and that can be for several reasons. Once again, this are only my guesses and I have not seen a photograph of the specific model tuner that you are referencing.....
The tuner is slowly filtering down into the smallbore prone and 3-p game, and if offering a tuner with a tube opens up a larger market, then it makes sense from a business perspective. (On a side note, I would be interested if the tube was dovetailed or drilled and tapped for a sight base. That may provide some insight to this theory as the provisions are there to mount sights.)
Aside from that, a tube in itself is an added weight to the muzzle, which as everyone knows will change the vibration characteristics of the barrel. Now if you are attempting to tune a rifle with an adjustable tuner, the only "advantage" of the tube is that you are essentially adding additional stationary mass to the muzzle.
There is also the theory that the addition of the tube acts as a controlled expansion chamber for the bullet to enter free flight with a minimal amount of external influence for the first few inches. In this situation, there would be a significant reduction in the wind's effect on the initial microseconds of flight.
Does this really make a difference...possibly - but it may be as much as a confidence level for the shooter as being able to be a measurable improvement for the stability of the projectile.
On the flip side, the addition of a tube can also have some detrimental impact to accuracy also. One aspect is that tubes need to be cleaned, as over time it can degrade accuracy. It is an excellent collector of partially burned powder and other miscellaneous crud and it readily coats the muzzle and crown much faster than without the tube.
Of all of the manufacturer's that offer tuners, how many companies make a reliable tuner and how many currenly offer the tube as a standard product and not an "option". (Note that I am not offering this question up as part of a position for or against the true value of a bloop tube on a benchrest rifle based upon the number of manufactures....it is only for my reference.)