Car is nice. It's handy, fast. You can transport loads or people, anytime you want. But – it's not so fast in queue, or in rush hour. And seldomly you need to transport goods or people. It pollutes and takes space. Usually bus or bike or feet are more handy.
Many have car, though. And once you have it, you'll use it. Your money is on it, and costs are running, even if car is stationary. Once you have it, you dont want to pay for busticket or bike.
If the car were cheaper? Or you wouldn't need to own it?
Why in tandem?
Originally, Delfiini was meant to be solo. But thinking of typical needs, when driving, people do occasionally transport someone else: girlfriend, spouse, child, or whom ever. So there was a need for another seat.
Side–to–side solution is obvious, and typically used. But there are some problems with it. Width increases air coefficient (by increasing surface and creating not so good form for vehicle (wide and short)). So this is against performance goals (so that you can use highways and join traffic smoothly).
Also, need for protection against side impacts is trickier to organize in side–to–side solution. To have the buffer zones for protection vehicle would be even wider and worsening the situation described above.
Tandem positioning gives a good chance to use passenger seat space also as additional luggage space. So small vehicle is roomy!
So bear with me - tandem seating is for your safety and comfort!
Of course, there are some wider visions included to this positioning.
Car traffic takes lot of space in cities. In some cities half of the land area! When most of the vehicles are replaced with shared Delfiini's (typically, there is one for about five users) it gives chances to take space from vehicles to people. But of course, this is a long-term vision.