It is a feature of Newmars. I had a 2000 Kountry Aire fifth wheel.
Newmar uses an electronic mechanism that is patented. I don't know if
they still do, but they used to guarantee the mechanism for life.  They
invented flat-floor slideouts, BTW.

As to why it's slow, I really can't tell you. All I know is that it's a
feature of their mechanism. I had my rig for 5 years and aside from one
or two adjustments to each of the two slides. There were no major problems.

The faster slides are usually  hydraulic.

Hi,
When I was looking at Newmar's I was told, (by a salesman) that Newmar
invented the flat floor slide out.  Which they may have.  He also said
that it goes so slow because it is very precise?  Between how slow it
was and the talking voice telling me the slide was going out, I was not
impressed :)  I've had hydraulic and electric slide outs.  Both moved
faster then the Newmar ones but both were not flat floor slides either.

It may be a feature but I didn't especially like it, especially the
talking voice and bell.  It takes about 30 seconds or less combined to
put out our two slide outs.  But then we have to stand there and hold
the button in too :)

Take care and Happy Campin...