You know there are lots of advantages behind the Single page applications, but just like other technologies it has some lacks in some cases. I just talk about disadvantages of SPAs in this post:
It makes the page content heavy and large: just image a single page apps which handles lots of feature in a page, needless to say it would be large and maybe in some cases it could cause page load slow.
Implementing Business logic in client side is cumbersome: you know in SPAs, most of the business codes implemented in client side, as you load the batch data and make some processes on them, so it would make it harder to read and maintain.
Powerful servers are required: I'm not sure about this but it seems that SPAs need powerful server(s) because dislike traditional we applications you have to fetch all the data at the first time when a user comes into the web site! (in traditional apps you respond for every request only)
SPAs are not crawled: making an SPA a CEO friendly one is not an easy task, it doesn't mean that there is no way for it. there are some CEO techniques to do that, take a look at this presentation for more info.
Tags: Asp.Net SPA