All is takes is a disruption (medical diversion, closure of FRA for 1-2 hours to whatever reason, cabin crew member going sick, congestion in FRA and missed slot, etc) and otherwise perfectly on time flight gets delayed/cancelled. Or, worst case: one counter open at T2 for immigration control and 100+ pax in front of you, all needing 1 minute to clear immigration. Why to
risk to save 100-200 EUR is beyond me…