That's a complicated question. Some people are scared to receive that type of love because they never got it or it can be taken away from them so they never trust it.
Some people have tricked themselves that it doesn't exist or that they don't want it. So they put up this hard shell to protect themselves even though deep down it's what they want. It's not a clear cut they don't want it from you thing. Everybody has their issues that hinder them or they're just in a bad spot in their lives.
Also everybody is not worth your love or emotions. Can't keep giving it away hoping somebody will take pity and give it back. It has to be for the right people. Don't be so eager to fall in love or give love to everybody you meet. You'll know when the person is worth it, trust me you just know that shyt.