Why is Loss on sale of fixed assets added back to operating cash flow?

It is added back in because it is an accounting expense, not a cash expense. So when you break down a Statement of cash flows you have three parts; Cash flow from operating activities (Think selling of goods), cash flow from investing activities (Think fixed assets) and cash flow from financing activities(Getting a loan, or issuing stock). We depreciate fixed assets (except for land, unless we are taking into account something like the amount of coal in coal mine). However like stated before, depreciation isn't a cash expense and if we look at an Income Statement we see that depreciation is one of the first things subtracted from the Income Statement balance and skews the Income statement. Hence the Statement of Cash Flows. So again, just think of it this way; it was money that was never really spent, so we need to add it back in.

Hope you are able to see what I'm getting at, sorry if I made it hard to follow or was to redundant.