Hmmm, Because they are not ready to make a commitment??.
There are so many possibilities that really, only that person, could tell you for sure.
I learned recently that liking someone is not the same as actually wanting to be with them.
(I knew this anyway.. I was more like reminded)
In the case of an NFJ.. It's probably because they don't feel like they can give you what might be needed at this time.
Tis a responsibility, burden. Or perhaps just turning you down in a manner where you don't feel the crush. If the choice of words were truly ''like'' than the latter may be the case assuming you proposed the relationship.
Sounds to me like that person doesn't want to have a relationship but doesn't want to hurt your feelings, either. So the solution would be to tell you they don't want a relationship in a polite and friendly way, as in 'I really, really like you...but...' - the 'but' doesn't have to be said, but it's there nevertheless. If I were in a situation like that, that's how I'd try to solve it.
I often tell people I really like them and mean it, as I do truly like people - but it's a veeery long way from 'liking' someone to having a relationship with that person.
We could learn a lot from crayons. Some are sharp, some are pretty and some are dull; some have weird names and all are different colours, but they all have to live in the same box.
type aside, there are several reasons why anyone would say this
1) they are not emotionally ready
2) they're going through a tough time and don't feel they could keep their end of the relationship
3) they're focusing on their finances first before they settle down/pursue a love life (this is my case)
4) they like you, but they're not attracted to you
5) they are attracted to you, but don't view you as good relationship material
6) they don't want the emotional commitment