Answer: Everyone isn't created the same, for example, some are more out spoken that others. Interests, relationships and dating have evolved over time, and many actions usually aren't as they appear.
Why do some guys "friend-zone" girls. First, the depends on personality of the individual involved.
1. Some might not be courageous to ask the lady out. Shy guys somethings have shaky hands and voice when talking to a lady they have an emotional pull to.
2. Some might have a feeling the relationship won't work out and are scared to try. Again I say, we are not the created the same; some people (guys) indeed are scared of complicated relationships!
3. The lady's association with another guy might make the "friend-zoner" think she's in a relationship or someone else has her attention. Therefore, if he tries, he feels there's a 'NO' waiting for him.
4. Here's a common one: Some guys hate rejection, are scared of rejection and run from anything that might bring it! (They feel friend-zoning makes them sure of if they are going to get a positive answer before asking).
5. Some guys are in currently relationships but do not love the lady (probably asked her out due to curiosity and experiment), and they find it hard to jump out. After meeting a lady he loves, he keeps her in the "friend-zone" hoping his current relationship crashes.
6. On the offside, some guys want many ladies, so friend-zoning keeps the ladies at arms length.
7. As you said, the guy might just "claim to love" the lady but really doesn't. If you love someone, you set things straight to get things levelled and rosy between the two of you.
Hope that helps.