probably this is different between different airlines and continents, and is definitely easier if you regularly fly with the same airline on the same route and know its flow, pricing and rules...

but generally in Europe many airlines will by default show you only the base fare price without carry-on bags, checked bags, seats, etc., and the surcharges aren't fixed (some flights may have cheaper bags, seats, than the others, on the same airline), and then there are multiple levels of "Economy" pricing with some of the options packaged into the price (e.g. Austrian has "Economy Basic", "Economy Light", "Economy Comfort", "Economy Flex"), but sometimes buying Economy Basic + baggage + seat may be cheaper than Economy Comfort.

Also the rules of what is included in which package differ from the route (longer routes have more included), and from the operating airline (e.g. Air France website also allows you to book lower cost Transavia flights, Austrian/Lufthansa websites also allow you to book lower cost Eurowings/Discover flights...)

And then there is the hell which is Ryanair, where you have to go through multiple pages of "no I don't want travel insurance", "no I don't want to rent a car", "no I don't want to buy fasttrack", "no I don't want to book a hotel with you", "no I don't want to buy a seat", "no I really don't want anything else"...

And all of these employ gray patterns like the "no I don't want it" button being less visible/prominent than the "I do want to pay more" button... (and this is not only true for Ryanair, but also for Austrian's "Upgrade to Economy Comfort" vs. "Continue with current fare", which conveniently shows before selecting if you want bags, seats, etc. where it actually could've been useful if it showed you that you can pay less)

Also most of the airline search sites don't allow you to filter non-stop flights, so if you're flexible on dates it will show you "cheaper flights" on other days, but instead of 2h flight from Vienna to Paris it's gonna be 5 hours because of a transfer in Amsterdam/Frankfurt...

What could be better would be "I want to select a seat at check-in, I want to fly with 1 checked bag and no carry-on bags, I don't want anything else, I want a non-stop flight, show me cheapest prices for this"...