WordPress eat your webhosting resource like crazy. Heavy WP Themes, lots of plugins, JQuery Libraries and MySQL Queries. Everything contributes to make things worse.
Even if you're using plugins to cache your WordPress sites, you need to know that, not every resources can be cached and you're still consuming resources when you are serving those pages.
If you're using a shared hosting account, you can get your account hacked or terminated at anytime if your WordPress sites consumes lot of memory and CPU Resources.>