Why do some model names use "MKII"?

I like Brf's response!
Some manufacturers tend to do this more than others.
Other just come out with a new model. Either way, it is the best way to raise prices!!
Like Manley just raised prices. They would have been better off to do a tiny bit of 'upgrading', then rename the product with the price increase. i guess they are just too honest!
Actually, one mkII took some parts OFF! the mkII of the famous Audio Research Sp-10: the mkII removed a device sitting in the middle of the circuit board, so you knew if the original was upgraded because the gizmo was NOT in it's spot on the circuit board. (I know because I owned a SP-10 upgraded to mkII) the other few parts changed really were not enough to warrant a name change, so the mkII designation for the Sp-10.
Worrying abot it is silly IMO. If a company is willing to do constant research to better thier products, why criticize them? Some companies make a product and then that is it. they stop dead. it's done, who cares...
Others continue to work on them, some do not even tell customers (like Bryston) that later serial numbers have 'better' parts or features, and others do.
(The Bryston I know of was a transformer upgrade ala Stereophile review of 7B-SST2 amps.. and that is not the only part that they have made better and just add it in the production. (Bryaton is not 'hiding' anything, they also are not advertising it either.)

Like kurt-tank said , it's just a newer version . Some call it mark 2 some add a letter or number some manufacturers give it a new name but it all means the same .

This also opens other doors, Upgrade your MK1 to a MK2. You really won't know what you were missing till you hear a MK2 whatever. Now there will be slight sonic difference between an MK1 upgraded to a MK2, than a brand new Full MK2. They might even offer a Signature Series MK2 for only 5k more. What a crazy hobby.

I think that many do pursue the ceaseless pursuit of improvement, sometimes parts become unavailable and new one's must be used. However, I do think that the basics of great preamp and amps design is pretty well figured out and has been for many years, though there have been some improvements in passive parts. So yes, there is a quest for improvement, but there also is a very power marketing reason for new models on the showroom floor.

Mark II was the second king of France.