Honda's downhill in Europe started in 2014-2015. What happened? Well, they stopped selling two most important vehicles in Europe: Civic (EU spec) and Accord. No manufacturer can compete without these models. Nissan and Honda are playing very dangerous gamble by offering only SUVs and compact cars. Why did Toyota grow in Europe? They made Avensis and Auris just for Europe.They are trying anything to maintain sales and not lose their dealer network i guess... you can see how bad the situation is in Europe, when Mazda and Suzuki outsell Honda 2 to 1.
They sell around 140k vehicles per year in 27 countries vs 750k for Toyota.
They did try in last few years with some special diesel engines, it did not work out... Gotta build it for Europe and it likely does not make financial sense for them to go all in, hence product portfolio that is quite niche.