I would rather say
But what there wasn't was many people.
***** NOT A TEACHER ****
Hello, Birdeen's Call:
1,
IF (a big "if") I understand your question, I think that the Master (aka Henry Fowler) would agree with you.
2. I do not know which edition you have of his masterpiece A Dictionary of Modern English Usage.
a. The second edition discusses this starting on page 691.
b. The third edition discusses this starting on page 839.
i. Some of the Master's fans feel that the third edition revised too much of the Master's teachings and that it is too permissive.
*****
3. I could not find any examples exactly like yours, but I believe that these following "correct" sentences from the
Master's second edition (which, I understand, faithfully followed the first edition in 1926) show the grammar that
interests you:
What is required
is houses at rents that people can pay.
What is needed
is a few recognized British financial corporations.
What is required
is three bedrooms.
*****
4. The very strict
Modern American Usage (1980 edition) is also very clear on this matter. Here are some of Mr. Wilson Follett's examples in the section of his book entitled "Number, trouble with":
What they saw
was the white sand cliffs on the eastern coast.
What these gentlemen need
is some new moral values.
*****
5. I end this post with this comment from the third edition, edited by Robert Burchfield, who truly had a "distinguished
lexicographical career" (as the book jacket says). Mr. Burchfield writes:
"There is an understandable tendency to let 'attraction' take its course in certain circumstances."
Perhaps that is the justification for the "were" in your quoted sentence.