I've visited Portugal only once, so my experience is very limited with the country, but public transport wasn't very good even in Lisbon in my experience. Don't know if there are portugese cities with better public transport, but if that's the best Portugal has, then your opinion is certainly understandable.
Not only that, Portugal sits close to the middle of the pack in population density, not far from France and their public transport is certainly only good in and around cities.
It still is undeniable that cars are quite costly. It would save Portugal money to actually invest in better public transport, maybe even make it free. Free or affordable public transport increases the frequency of buses as the ridership increases.
The biggest difficulty is changing the public perception of cars as a status symbol and the feeling of "freedom". The freedom one gets from free public transport is difficult to comprehend, I think. One can just hop on the bus, step out at a random place, rent a bike, explore, and hop onto the next bus with barely any planning except for getting back.
In France, the number of visits people made to shops outside of the center actually increased.