It is probably a silly question. By the end of 19th century, several branches of physics like electricity and magnetism were fairly advanced. Maxwells equations came in 1965. Lenz's law came in 1834 etc.

However, blackbody radiation comes very late to party - Wein's law appearing only in 1894. I mean plotting the spectra of a hot object seems like a fairly straightforward process - something that even Newton could have done.

What am I missing? Maybe constructing a blackbody is very hard and the technology didn't exist earlier or maybe it just wasn't an interesting area for the physicists before?

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Edit: I am also confused about this statement in a book I am reading: "Classical theory indicated that energy should be a monotonically increaing function of frequency, diverging as frequency increases without bound. All materials should radiate infinite energy per unit time"

Can someone explain how classical theory predicts this?