and I think it depends on the company.
For Round2 it probably depends on sales. I think they do a small or moderate run, and see how it sells. If it does well they keep ordering more runs until the sales drop off. Revell may have done something similiar, but there's no way to tell what they are doing now.
Some companies like Hasegawa and Fujimi do Limited Edition kits, very short runs, and they seem to go fast. Especially car kits.
I think very few companies leave a model in continuous runs.
Not like the AMT USS Enterprise (Star Trek) that stayed in production for decades from around 1966 all the way to the 1990s continously.
That might have been a near record.
But I believe nowadays when a kit pops out you have to get them right away. You never know if it will vanish for decades again, especially if it didn't sell well.
That's my opinions.