Sorry for the long write up.
So to follow up with what was said earlier, the main reason is because Symphonia was like final fantasy VII to series because this was the entry that essentially put the series on the map in the west. The game went from a series that was essentially Japan only (heck, we still haven't gotten certain titles that were japan only) to a series that got regular western releases. It says more then I ever could that Symphonia is STILL the best selling tales game in the west, which was confirmed by a director in the Tales team unless Zesteria and Beseria beat it, even though the game was released in 2003.
As for why it is talked about a ton more, there is a lot of things that push people to believe Sakurai (who still has the final say) would pick Lloyd over anyone else. First, in an interview Sakurai has outright said when choosing the tales rep to get a mii costume " I really think it has to be Lloyd here", meaning Lloyd we know is at least on his map compared to other protagonists. Second, out of all the tales characters that would be considered, Lloyd definitely has the most history with Nintendo, having his best selling game be a Gamecube exclusive for a time and the sequel to the game also being a Wii exclusive. This is the main reason he gets mentioned a lot, as he is the safe Nintendo pick, that would logically make the most sense for a lot of people. Finally, as I mentioned earlier, Symphonia is still the best selling Tales game in the west, which means he probably also the most global appeal, which I personally think is pretty important for a game like Smash bros.
Within the core fanbase, things get muddied up. Like a lot of fandoms, the East and the West don't always agree with what the most popular character/title is. While symphonia was really popular in the west and Lloyd himself is loved by the western fanbase, the most popular game in Japan is probably Tales of Destiny and the most popular character is either Leon from Destiny or Yuri from Vesperia. That is why Yuri often gets mentioned on Smashboards, as he is extremely popular in Japan. Do I personally think popularity within the fandom gets considered when choosing a fighter to represent a series? No, as Joker himself is less popular then the P3 and P4 protagonist(Online poll Atlus did for persona Q2), but it is possible they might consider it. Personally, I'll be happy if we get any Tales character, but I have my fingers crossed for Lloyd.