That and the fact that the GDPR had racked up so much foreign debt that, at the end, it was borrowing money to meet the interest payments. That is not (to put it mildly) a sustainable economic strategy.
And your Sources are???
The GDR was the most export oriented economy of the Eastern Block States.
It's balance of payments was mostly positive till 1986.
What broke the GDRs economic back was the rising oil-prices and the economic collaps of the other Eastern Block States.
Import prices for crude oil from the USSR increased 11-fold between 1974 and 1986, and natural gas prices seven-fold.
Soviet supply shortages had a heavy burden increased the external constraint on imports on a forreign currency basis with relatively high interest rates.
The western credits increased the GDR debt and interest charges in foreign currency from 1975 onwards.
However, the GDR had met its payment obligations to the West until the very last minute and in the end suffered no credit refusal from the West Banks.
Sources:
Deutsche Bundesbank, „Die Zahlungsbilanz der ehemaligen DDR 1975 bis 1989“, August 1999.
Heske, Gerhard, „Bruttoinlandsprodukt, Verbrauch und Erwerbstätigkeit in Ostdeutschland 1970-2000, Köln 2005 (Zentr. f. Historische Sozialforschung, Supplement No. 17)
Luft, Christa, „Die Lust am Eigentum“, Zürich 1996
Wenzel, Siegfried, „Zur Rolle der Ökonomie im finalen Entwicklungsabschnitt der DDR“, in: Pankower Vorträge, „1989 – 1990. Die DDR zwischen Wende und Anschluss“, Berlin 2000, Heft 20
Wenzel, Siegfried, „Zur Rolle äußerer Faktoren für die ökonomische Entwicklung der DDR“, in: Pankower Vorträge, „Die DDR-Wirtschaft in den 80er Jahren“, Berlin 2005, Heft 70