The reason some eyepieces are better suited to one scope type than another has to do with the way different telescope designs come to focus.
We first think that a scope comes to focus at a single point. Well, it does if the point is a single star. But there are stars across the whole field of view! not all in the one spot. So, each star really is an individual point of focus which really is a focal plane, not single focal point. AND this focal plane is NOT FLAT, but curved, somewhat like a bowl.
The shape of this curve is either concave or convex, and which it is is determined by the design of the scope - Newtonians give a concave focal plane, refractors, SCTs and Maks produce a convex focal plane.
Then, how "deep" the focal plane/bowl shape is is given by the focal ratio - the faster the focal ratio, the deeper the bowl shape, the slower the f/ratio the flatter the shape.
A clue to this is given by the use of "field flatteners" in astrophotography. The chips in cameras are flat. But as the scope produces a curved focal plane, an image produced by a neat scope will be sharp in the centre of the chip but become increasingly out of focus further out from centre. A field flattener alters the light path coming from the scope so that it is in focus across the whole chip, effectively flattening the focal plane.
Eyepieces in turn are first designed with a particular focal plane shape in mind. As it is, it is easier and cheaper to design and make an eyepiece for a convex focal plane than a concave one. And so, an eyepiece will work better in one scope/focal plane than another. This is called "optical matching".
If you use an eyepiece in a scope that is not an optical match, you will see a number of aberrations such as astigmatism, pincushion, spherical aberration and also field curvature.
Not understanding optical matching and you will find many people dismiss a whole eyepiece line as "crap" when really they used that eyepiece in the wrong scope type. There are so many eyepieces lines and brands dismissed as rubbish because of ignorance. Use these same eyepieces in the correct scope design, and they perform brilliantly. Funny that, eh!
Now, with the complex nature of contemporary eyepiece designs, you will also find that within a specific eyepiece line thats firstly designed for a particular focal plane, you may find one or more individual focal length pieces that will actually do a very good job also in the very focal plane shape they are not designed for. They may not be "perfect", but the aberrations will still be very well controlled so to be quite acceptable (depending on what you are prepared to accept).
Take the Baader Hyperion line. These are specifically designed for a convex focal plane - refractors, SCTs and Maks. In these scopes these eyepieces are brilliant. However, in Newtonians all of these are poor to very poor performers, and the visible aberrations become more significant the faster the focal ratio gets. HOWEVER, the 5mm Hyperion actually is also brilliant in Newtonians, including very fast ones such as f/4.
Ok, this explanation is quite long, but it is enough to start seeing how there is more to eyepieces than "this is a scope, this is an eyepiece, so it will work..."
Nothing wrong with this at the start of your astro experience. I too thought exactly like this too. But as my experience grew, so did my awareness of performance differences and ultimately being made aware of optical matching and the oddity of contemporary eyepiece design that can give brilliant eyepieces for bugger all cost
But it takes time to learn.
Alex.