I thought Lorenz was fairly attractive when he married Astrid. And he is really, really tall, always a plus for a man imo.
Astrid fell in love with him when she was a teenager. I think I remember reading that the BRF, King Baudouin in particular, was ecstactic
that she was bucking the trend among her peers and was not
marrying a commoner.
The Belgian RF are apparently very old school in their attitudes toward marriage partners. As it stands, they will probably be the only Royal House left in the Gotha whose hereditary line remains exclusively Aristo/Royal.
The fact that it was a real love match was icing on the cake for them.