They do actually work. Your example uses amplitudes and frequencies that may be hard to hear. Also, more importantly, Csound will finish if it only has instruments with negative durations. At a minimum, in a case like that, you need to force Csound to keep playing. Changing just the relevant bits from your example:
instr 1
asig vco2 0.1, 700 ; easier to hear
out asig
endin
</CsInstruments>
<CsScore>
i1 0 -1
e 2 ; runs for 2 seconds
</CsScore>