Official Deutsche Bahn figures are likely underreporting the extent of the problem as the reported times and actual timetables are -aggressively- out of sync (to the frustration of many riders).
It's hard to dissect the true source of the problem as there are various factors at play. However the central cause is starving the system of funds. This presents a strong warning for countries that are trying to encourage the use of public transport in order to meet their climate goals.
Some detail is available here: https://www.dw.com/en/germany-whats-wrong-with-the-deutsche-...