Telecos are a weird example. They're more like a utility than a product one can live without. This, combined with the massive duplication of effort competition would entail, is the reason why they are so intensively regulated. Oftentimes the government provides funding & loans[1][2], and tax incentives for telecom infrastructure buildout.
For what its worth, the reason telecoms have such low margins is that they are a commodity (which in my opinion, is what they should be). Their lobbying to get the ability to give non-neutral lanes is to give themselves a way to not be a commodity. I don't really see the upside for society as a whole for them to be essentially granted a state monopoly and then decommodify themselves to make things that were cheap more expensive and risk the internet in the process.
Their profits are nearly risk free even if they're relatively low. According to your link, the average return was between ~2% and ~11%. We're not talking about fractional percentages here. A small low risk margin on a lot of money... is still a lot of money. Notice that the ROIC in exhibit 3 lines up nicely with utilities.
I'm not sure where you were getting your info from about wireline divisions, but I found this interesting report: http://marketrealist.com/2015/01/wireless-telecoms-key-indic... It looks like investment in wires has declined by about 40%, but investment in wireless has increased tremendously. I don't know what the absolute numbers are though. I imagine wireless is much cheaper to deploy.
[1] Government funding of rural infrastructure - https://www.usda.gov/wps/portal/usda/usdahome?contentidonly=...
[2] Government funding of certain consumer uses (which is free money for the telecos) - http://www.gillibrand.senate.gov/imo/media/doc/Gillibrand%20...