That's just an excuse. There are disposable plastic cups that are used widely within non-Catholic denominations for hygiene reasons.
I'm sure the cup manufacturers would not object to the added business from the Catholic church should they decide to celebrate communion with the laity the way Christ commanded without drinking out of communal cup.
First, I don't believe believe that there were plastic cups the Church could have used in response to the Black Death.
Second, you are again demonstrating either a profound ignorance of the nature of the Eucharist or are again projecting the symbolic grape juice into the Catholic Liturgy. The spillage, or misuse of even the smallest drop or crumb of the Host of either species is a sacrilege. To the Church is it far more serious to casually treat the remnants of the Precious Blood of Christ left in the little plastic than if you disrespected your dear Aunt Tillie by putting her body out on the curb for the Wednesday trash pick up. This is specifically addressed in the GIRM (General Instructions of the Roman Missal:
Paragraph 279 of the GIRM: The sacred vessels are purified by the priest, the deacon, or an instituted acolyte after Communion or after Mass, insofar as possible at the credence table. The purification of the chalice is done with water alone or with wine and water, which is then drunk by whoever does the purification. The paten is usually wiped clean with the purificator.
Peace be with you.