If you're going 50km/h on a bike line, absolutely no one driving car is expecting you to arrive to the crossing in 3 seconds from 50 meters away.
You absolutely have to slow down to a crossing on a bicycle, motorized or not. And this is coming form an cyclist who doesn't own a car or a license.
Edit: also if you're speeding like that on bike lanes where others are going on average less than half your speed, you're causing danger to others.
Ride like maniac and die like maniac
You forgot to account speed. Trains go something between 20-40+ times (or far more if you account carriage) faster than average person walking. This increases the throughput of the lane massively.