Amazing Photo: 842 priests ordained *simultaneously* in Barcelona

With a papist tip of the hat to the Blog of the Courtier, the New Liturgical Movement on what has to be a singular event in ecclesiastical history - and one for the record books:

[This is]the simultaneous ordination of 842 Priests which took place at the XXXV International Eucharistic Congress of Barcelona in 1952. In the Olympic Stadium of Montjuich, 21 altars were erected, at which 21 bishops celebrated synchronized Masses during which they ordained about 40 priests each. The bishop of Barcelona, Mons. Modrego Casáus, celebrated at altar 12, and his voice was amplified by microphone throughout the stadium. In the middle, a schola of 300 seminarians from all across Spain led the people in chant.

As Gregor sagely notes at NLM:

Interestingly, the practice of "synchronized" Masses was forbidden by the Instruction "De Musica Sacra et Sacra Liturgia" of 1958 (no. 39), only 6 years after this high-profile celebration.

Gee, can we guess why?