Because a decison hasn’t been made, and seemingly can’t be made, namely, what deal do we leave with?
Is the majority decision a hard brexit, a soft brexit, a BINO, Norway plus or minus, some other bespoke deal?
As there has been no decision made as to how to leave, then yes, a 2nd referendum is imho necessary to ask people to agree on the deal offered.
They should structure it:
- Stay in the EU, revoking Article 50 and going back to the situation before June 2016?
- No deal Brexit
- May’s deal (with backstop)
- Norway plus
And then see what the majority want.