Since LH, LX,... have introduced the light, classic, flex fares in Eco, the websites normally only display the cheapest available booking class.
LH and LX managers at events told me that >95 % of the people want to book the cheapest available fare, so higher booking classes are not displayed anymore.
If you want to book higher booking classes, you need either to call the airline or book at an airline ticketing desk at the airport or through a travel agent.
Personally I normally book via my travel agent.