It's both - they are pandering to the lower-income folks AND believe it's a good thing.

If designed properly, and combined with pay systems and insurance, "universal" health care doesn't have to be a bad thing.  Basically, we already have a form of it - it's just really inefficient.  Right now, people without insurance STILL get medical treatment, and YOU still pay for it.  They either get MedicAid or MediCare, which is paid for with your tax dollars, or they go to the ER and then don't pay - in which case it is paid for by your higher insurance premiums and higher hospital bills.  So it's not like people without health insurance aren't getting medical care now - so if a "universal" system makes the whole mess more efficient, but still allows private insurance, then it would actually be an improvement.

Of course, more likely, politicians will fuck it up.