Why were Byzantium, the Balkan countries and Western European crusaders defeated in the fight against the Ottoman Turks?

We are talking about the period of the XIV-first half of the 15th century, that is, from 1300 to 1461, when the Turks captured the last fragment of the former Byzantium – Trebizond (Constantinople itself was taken in 1453), they fled the crusaders in 1396 near Nikopol and in 1444 near Varna.

The reasons were as follows:

Internal conflicts in Byzantium itself, in the XIV century, they resulted in a civil war.
Conflicts between Slavic states in the Balkans.
The number of troops of the Ottoman sultans, as a rule, was higher than that of the opponents.
The Ottomans had quite strong artillery by 1453.