What? It was done because it was cheaper than the safer option? Say it isn't so...
I suspect you know the answer.
In the 90s and noughties, I did a lot of campaigning on local and national issues, including motorway widening. I can confirm that additional lanes AND retention of the hard shoulder was discounted due to costs. In my area, it would have led to a huge compulsory purchase exercise and wholesale demolition of communities. This was the plan put forward by the Highways Agency in the early to mid nineties, indeed some properties locally were purchased and blighted as a result, but the scheme was abandoned, to be replaced with the SMART scheme, which(as previously stated) did not include the vast cost of widening elevated sections and cutting away embankments. Once officially abandoned, the properties appeared on the market and were subsequently sold as dwellings again