A theory on why you're asked IF you would marry but never asked TO be married
Realize people are so different and can have a number of innocent reasons to apparently be getting a feel for where your mind is at. Assume their intentions are good but don't assume you know precisely the reason why. To know the precise reason why not ask them? Yep its that easy. However if you choose not to, or dont get a straight answer I again suggest you assume their intentions are good and leave it at that.
If in time a different reason from what you had expected and especially had hoped for is revealed you risk disappointment. There is one theory why you may be asked questions such as "would you be interested in dating" and "are you (would you be) interested in our getting married." I'll leave it to you to decide if the intent is innocent, deliberately done for personal gain at your expense, or to mislead you to believe something false.
A theory is that some people are egomaniacs. Its not about you. They are not trying to hurt you by deception. They only wish to stroke their own ego and only wish to hear your opinion to confirm that you want them. They may have no intent on following through on the suggestion.
If you have this person in a position where they have something to gain by being involved with you they may at times ask these hypothetical questions at a time they feel you may be growing cold with your feelings towards them. This in their mind can be an effective tool in reeling you back in. Again they may not be trying to hurt you. Again its about them, about their needs being met, and doing whatever necessary to keep that assistance coming.
I do not write this way to be a killjoy to anyone. I want everyone to pursue fulfilling and lasting relationships. However I want them to do so with their eyes wide open. Because when you follow down a path blindfolded, it is easy to step in shit. Do not expect what I am theorizing to happen nor expect things to happen as you want them to. Hope for the best and be prepared for anything less is all I ask. Doing so will allow you to more easily rebound come what may.