Einstein seems to be so conveniently dismissive that he knew about the seminal Michelson-Morley experiments but he probably knew about it too well [1].
Einstein is not the first great scientist who are in denial of other important prior contributions, and he also not the last one. Newton also probably knew too well about Al-Haytham (Alhazen), arguably the father of modern science, and his breakthrough experiments but never directly cited Alhazen's works in his seminal books on Optics.
[1] Millikan, Einstein, and the Birth of Relativity (4 letters):
https://www.aps.org/archives/publications/apsnews/200403/let...
"Abraham Pais, who knew Einstein well and wrote his scientific biography, was certain that Einstein did know about Michelson's experiment before 1905. He points out that Einstein was over seventy and in poor health when he spoke to Shankland; at the first interview he probably did not remember that Michelson's experiment is discussed in Lorentz's 1895 monograph, the famous "Versuch", which Einstein had definitely read before 1905."
Was the ethical requirement to discuss and acknowledge predecessors work as developed in Newton's time as in our own? I would naturally expect not because it would seem to me to be the kind of thing that develops over time, but I could be wrong as I am not a historian of science.
John Maynard Keynes is famously quoted as stating:
We seem to have come around to a new magical age.
It's a not a requirement, it's just a natural to do as a research scientist and a student of knowledge to acknowledge prior contributions if you knew it. The same is true when you are at the time of Aristotle.
while I said I was not a scientific historian I am well enough read that I can say no, the tradition of citing all sources is a relatively modern invention. Definitely not widespread in Aristotle's time, and not extensively practiced by Aristotle himself who very seldom names any source and their work, but I was not sure if in Newton's time it was already beginning to be established as I have not actually read many scientific papers from that time (some philosophical, but not science)
Furthermore I can't help but feel some logic would lead us to conclude it is not natural to cite, why? Because in our time if you do not cite your sources in a lot of occupations dealing with knowledge you will be punished for it. It would be absurd to construct punishments for failing to do what people will naturally do, and to have those punishments so often called on.
Even if we give a very lenient interpretation of not citing sources we would probably have around 10% of papers with errors, and that is with the fear of punishment.
Citing when one should and accurately is not normal, it requires discipline to do it, or there would not be such a high failure rate at doing it.
You need to differentiate between citing everything, and citing a select few prior works which are integral to your own. For the latter, it is very natural to mention and cite them, unless you have motive not to do so.
"Forgive him, for he believes that the customs of his tribe are the laws of nature!"
It reminds me a bit of an anthropology question I've heard brought up a lot that's sort of the dark inverse of xkcd 1053 [0], that many things that "everybody knows" tend to get lost over enough time. You don't need to properly cite experiments or lectures or books that "everybody knows". Especially when the work you do essentially replaces those things in the canon, such connections sometimes get entirely lost. To an anthropologist working in some ancient language the variations of the phrase "as everybody knows" are often a missing or lost citation today. The places where it is so implied that you have the same education or background or textbook as the author to not even warrant an "as everybody knows" is an ever worse thing because you don't even have the marker that you are missing a citation.
[0] https://xkcd.com/1053/
See also this article, which discusses transcripts from lectures given by Einstein in Kyoto and Chicago in 1922 and 1921 (respectively), and letters from 1899, with earlier accounts of the Michelson-Morley experiment influence:
https://arxiv.org/abs/0908.1545