fascinated by the presence of the past

In early-twentieth-century England, it was fashionable to claim that only a completely new style of writing could address a world undergoing unprecedented transformation— just as one literary critic recently claimed that only the new “aesthetic of exploratory excess” can address a world undergoing…. well, you know. Yet in early-twentieth century England, T. S. Eliot, a man fascinated by the “presence” of the past, wrote the most innovative poetry of his time.

I am not clear what does “fascinated by the presence of the past” suggest?. What is it in “the presence of the past” for which the man should be fascinated?

I believe it’s about " The Waste Land".
“Eliot’s poem loosely follows the legend of the Holy Grail and the Fisher King combined with vignettes of the contemporary social condition in British society. Eliot employs many literary and cultural allusions from the Western canon and from Buddhism and the Hindu Upanishads.” /Wikipedia/

His devotion to the gems of the past, their “presence” (actuality) that he admired, unexpectedly (?) resulted in the “one of the most important poems of the 20th century”. And the most innovative, each of the five sections of which could be read as a separate poem.
That’s how I read it.

Thank you, Eugene2114. It’s really helpful.