I think that this is less of a problem in Paris, but it's crazy in some other places. I used to live in Swansea, and for the last few years I lived there the cost of a day ticket was less than most fares (which the drivers knew, so they'd give you the day pass if you asked for most things). At £2.30/day, it wasn't too bad, but for 3-4 of you it was often cheaper to get a taxi. We went back a few months ago and it was cheaper for one person to get a taxi for shortish hops than to take the bus and the cost of the day tickets had gone up enough that it wasn't worth it.
The city council had spent millions remodelling the city centre to allow larger bendy busses when I was there. I never saw one more than 50% full and apparently a year or two ago they discontinued them. If they'd spent the same amount of money on more frequent, subsidised, minibuses, treating it as infrastructure that encourages people to do things that raise tax revenue rather than as a profit centre, then they'd have had far more people using public transport. Instead, privately owned bus companies have made a lot of money and it's now at a point where it's cheaper to drive than to take the bus.