The reaction doesn't "require" 120C, that was simply the first experiment they described. They began by confirming that this reaction actually takes place and discovering which PFAs were neutralized by it. To that end they boiled a mixture of the stuff for 24 hours.
The reaction can occur at more moderate temperatures. There is more analysis (with experimental results) further down in the paper:
> Substantial defluorination still occurred when the isolated PFOA degradation product (perfluoro-1H-heptane 2) was subjected to degradation conditions but heated to only 40°C (table S3).
Okay, but you can't, for example, heat up large masses of contaminated dirt to 40° without killing everything in them. And you probably can't even saturate them with DMSO, both because even though it's relatively nontoxic it's not that nontoxic, and because it's expensive.
The reaction can occur at more moderate temperatures. There is more analysis (with experimental results) further down in the paper:
> Substantial defluorination still occurred when the isolated PFOA degradation product (perfluoro-1H-heptane 2) was subjected to degradation conditions but heated to only 40°C (table S3).