Since "anyone lived in a pretty how town" was published in 1940, I think cummings intended it to represent American towns in the late 1930s and the early 1940s. This was during the last years of the Great Depression. Given that this poem was partially a criticism of people who focused only on the mundane, daily activities of life (rather than more meaningful things like culture, art, philosophy), I mention the Great Depression because this was a time when people had to focus on daily things like looking for work and trying to make ends meet. But this criticism of being occupied by the quotidian is just one theme.
A second theme is really a paradox and therefore two themes which contradict and support each other. Most people lived (and live) in "pretty how towns." "Anyone" could symbolize a particular person or it could mean anyone at all in that town. Representing one person in particular, the poet shows how only one person (noone) noticed and loved him. Everyone else in town were so preoccupied with their own lives ("someones marrying their everyones/ laughed their cryings and did their dance"), that most people didn't notice or only gave a passing glance ("one day anyone died i guess") when anyone and noone died. This pun on "no one" shows that the others viewed anyone and noone as nobody important: no one.
This is the nature of living in a town or a city. You recognize people who are close to you but don't and can't give the same time and energy to everyone else. If "anyone" means anyone at all, then we can say that anyone (everyone) has their noone (significant other) and all those anyones are only mostly noticed by their noone. You love some people and some people are simply not a part of your life.
e.e. cummings was purposefully ambiguous on the pun that "anyone" means a specific person and that "anyone" can mean everyone or anyone at all. Thus, everyone is subject to this paradox of the human condition (aside from celebrities perhaps) that we are noticed by few, ignored by many.
This goes back to another interpretation of the first line which is to say "how can anyone live in a pretty how town?" Sure, anyone has a noone to love them, but how does anyone deal with the alienation and loneliness with respect to being neglected by everyone else. The repetition and inversion of "sun moon stars rain" and "summer autumn winter spring" express the poet's desperation that time is passing quickly and nobody seems to stop and consider other people or ideas beyond the close tight-knit circle of their family, friends and jobs. This poem seems like it must be a description only of small towns but that is just the pastoral quality of how the language reads. It could equally apply to cities.
You might say that one theme is how life is fleeting; the poet questions how anyone can love those closest to him/her so intensely and yet not notice other people, not notice their passing as time flies by. A second theme is that, as cummings observed in American towns at this time, everyone feels alienated - everyone is an "anyone," making another theme about alienation, particularly in the modern (then) American town.
If you use this response in your own work, it must be cited as an expert answer from eNotes. All expert answers on eNotes are indexed by Google and other search engines. Your teacher will easily be able to find this answer if you claim it as your own