why can i not update from ios 5.1.1 to anything more current on my ipad?

You probably have the 2010 1st gen iPad.

That first model iPad had a short life, (considered an underpowered, early adopted model) and ended its iOS support at iOS 5.1.1.

If you need apps for that iPad, you can try to download the latest app from the iOS App Store and if the developer has left an older, compatible version on Apple's app servers, then you will receive a small window pop-up prompt that states that there is an older version of the app that is compatible with your device. Would you like to download this version now.

Tap the OK button just below the prompt.

FYI,

Not every app you attempt to download will have an iOS 5.1.1 compatible version. For older apps that may still have an older iOS version available, the lowest compatible iOS version of an app is iOS 4.2.1.

The search for iOS 5.1.1 compatible apps will be trial and error, but they are out there.

This website may help you locate the apps you can use with your original iPad 1

http://findoldapps.com/us/any_category/5.1.1/ipad/updated_date/desc/30/1

My 2010, iPad 1 has over 100 apps on it that are still functioning, but older versions of apps that I currently run on my newer iPad models.

If you need a more current iOS version or more powerful and current iPad model, you will need to purchase one.

Currently, the cheapest, new iPad that Apple sells is the new for 2017, 32 GBs storage, 9.7 inch screen iPad 5 for $329 U.S.D..

Found here.

https://www.apple.com/ipad-9.7/

Good Luck to You!

It sounds as if you have an original iPad (the one without a camera). If so, it can't be updated past iOS 5.1.1. If you want or need a later version of iOS, you'll need to buy a later model iPad.