Due to its resistance ti is easier to get reasonable sized builds that are still mechanically durable.
The concerns with vaping off ti are FUD mongering. Grade 1 titanium has been advocated by mmj doctors as a means of vaporizing full melt cannabis concentrates for a few years now.
In APV use ti doesn't approach oxidization temperatures. Even if it did, ti is one of the most hypolergenic metals. Titanium dioxide has been used as sunblock for decades. Granted, external use != internal, but given no/little oxidization is occurring during nicotine vaping and titanium is used for medical implants... I personally feel the fear is far overblown, especially coming from a crowd of people that for the most part smoked cigarettes knowing the proven danger.
Another angle is that the aerospace industry has been welding titanium for decades. If there were the same health risks associated with the welding of materials like galvanized steel there would have been evidence a long time ago.