Learn English – Are the feelings always a noun

For the same reason "the pen" in Spanish is "la pluma", while "the pencil" is "el lápiz" instead of "la lápiz": it sounds more natural to native speakers (as StoneyB mentioned in the comment, we're 'voting' on how to use these words).

Note that if you mix these up you'll probably get a few funny looks, but you won't be misunderstood.

Often the countable and uncountable versions of an English noun will refer to different things. For example, "hamburger". If you say,

I love hamburger

it means that you enjoy the actual ground meat, in all its various uses. On the other hand,

I love hamburgers

means you like the specific use of ground beef in a hamburger, with the bun, lettuce, pickles, tomato, etc. You can also say:

I love a good hamburger

to refer to the specific object, with the relevant qualifiers.

In a similar way:

I love chicken (the meat)
I love chickens (the animal)

I love television (the programs on television)
I love televisions (the electronic device)

These distinctions seem idiomatic and can only be learned by exposure, memorization, and practice.

However (in general) when a noun's countable form and uncountable form both refer to (more or less) the same thing, it seems you use the uncountable form to refer to the generic or overarching concept, and you use the countable form to refer to specific instances or examples of that thing. With cake:

I love cake (cake in general)
I love the cakes Mary served at her party (those specific cakes)

I love coffee (coffee in general)
I love the coffees from Brazil (the various varieties of coffee from Brazil)

Note also a similar use when talking about wishes or desires:

I'd love some cake.
I'd love a cake.

As with anything in English, there may be exceptions.