Because potty training is just the first step, isn't it? The little-butt-perched-on-big-toilet issue lasts a bit longer. Also annoying is having to fiddle with portable potty seats when YOU have to go to the bathroom. This would have solved both problems!
For less than $40, this is an amazing value for the level of convenience and peace of mind.
At Amazon: Mayfair 186CP 000 NextStep Built-in Potty Seat with Non-Tarnish Chrome Hinges, available in round and elongated styles, $35.03