They could've said "no, fuck you, we have enough funds to keep paying interest, we don't need to borrow any addl funds. Either roll over the existing debt or we'll default and you'll get nothing."
Why didn't they do that?
By the time Syriza was elected it was too late for that. The prior government had already implemented a host of Eurozone austerity demands which then drove the country from a primary surplus to a deficit.
No, the reality is the bailouts, debt forgiveness, and modest government reforms converted a huge primary deficit in 2009 to one that was small enough to allow socialists and their apologists to fudge the numbers a bit to claim and/or forecast a primary surplus but there was never actually much of the sort of surplus that actually showed up as cash in a bank.
And also whatever damage a modest primary surplus may have caused Syzira is now plotting a course that will be many times more destructive. People waiting in line for an empty ATM in hopes of getting their money to the safety of their mattress are neither particularly good for production or demand.