Well, this one is a bit difficult to answer with the amount of detail you have given, or without getting out the spy gear and watching you with some guy you are interested in. So, if it is a swing and a miss, forgive me, as I shall have to stick to generalisations here.
First possibility. You are picking the same type of guy each time. The sort of guy that needs a girlfriend as validation more than as a partner. They exist. They are needy morons. And not worth wasting your time on. This one is unlikely, unless you are really, really, really bad at picking partners.
Second possibility. You are naturally undemonstrative. Someone who, being told they are going on the romantic trip of a lifetime, smiles slightly and says "That is nice." No crime there, in fact it is handy if you plan to commit any crimes. But in a relationship, it is hard work for the partner, who feels immensely unappreciated. Fortunately, enthusiasm is slightly easier to fake than an orgasm, it just takes practise. If this fits you, start practising. Watch America's Next Top Model, or Clueless, and make notes on how to react - then tone it down by about 50%.
Third possibility. You are as exciting as cold porridge. Ask one of your female friends about this. They will be delighted to list your shortcomings in great detail.
Another alternative:
You keep picking guys with love languages you don't understand. This makes them feel like you are not interested even though you are showing interest in the manner that makes you feel interested in.
There are 5 love languages:
Words of Affirmation, Quality Time, Receiving Gifts, Acts of Service, Physical Touch
This is a tough one! For example, I am absolutely for certain Physical Touch. Hugs, kisses, back rubs, etc, etc,
Because of how I was raised I also saw a lot of Receiving Gifts and Acts of Service so they also come naturally to me, but I did not see much Quality Time or Words of Affirmation. This makes me a bit "stunted" on how to love a person who needs these things.
Every time I dated someone I would subconsciously do those things that come naturally and those things I learned as manners of saying I love you. However, when I dated some people that were Words or Quality Time, they were often confused about how I felt about them, because I didn't show either of those 2 love languages to them. The gifts, and touches and acts were nice, but not "love" to them.
You should examine which love language makes you feel loved and which other ones come naturally (like they were your parent's love languages) and see if you find a pattern.