There are way more poems than there could be monuments, simply for the sake that poems are easier to create than monuments.
A monument, if created well, like the Great Pyramids, can last throughout multiple civilizations. A well created monument does not require active maintenance. The monument exists whether someone cares to show it to someone or not . Therefore, unless someone or nature destroys the monument, then the monument will continue to exist.
A poem, on the other hand, requires active participation. Once you write a poem, you'll have to spread it to other people, and they would have to then spread it, and so on. Without that spreading from generation to generation, and from civilization to civilization, the poem will die out.
Hence, if one monument was created, and one poem was created, the monument will outlast the poem. The monument takes more effort to create, but less effort to exist. The poem, however, takes less effort to create, but more effort to exist.
Well since you took it their, pyramids are the oldest monument in existence, and we have poems from ancient Egyptian times, so that pretty much proves that the too can survive thus far, however, the pyramids have long since, lost much of their original purpose, physically, mentally and spiritually, and in this way they will eventually fade into dust, where as the ancient Egyptian poems haven't even lost cultural significance, relevance or importance, as they are still not only beautiful and works of art but also extremely empowering.
Thanks to the technology, Nowadays, preserving poems takes much less energy than keeping new-built constructions. Imagine the time you create a poem afterward you could simply convert it to some digital information by typing , scanning and so on ... In this situation I believe preserving digital information would be much affordable than retaining a gigantic structure .
However these days you could barely find constructions which are designed to last for more than 1-2 century!!!