Jalebi is one of the few Indian sweets almost never sold from a sealed box. The vendor pipes, fries and dunks it while customers wait, because the product has a very short window in which it is what it should be.
The texture depends on a shell that is still crisp
A jalebi is fried until its outer surface has dried and hardened, then dropped into syrup. The shell absorbs syrup while holding enough rigidity to crack when bitten.
That crack is the entire point of the sweet. Everything inside is sugar syrup, and without the shell what remains is simply a sweet, wet coil of batter.
The shell begins softening as soon as it leaves the syrup, since absorbed liquid keeps migrating outward. Within an hour or two the contrast has gone completely.
Syrup temperature has to be managed continuously
The syrup sits in a wide pan beside the fryer and is kept warm rather than hot. Too hot and it soaks in until the coil collapses; too cool and it coats without penetrating.
A vendor working a live counter adjusts this by feel through the day as the syrup thickens with evaporation, thinning it with water once it starts clinging to the ladle.
None of that adjustment is possible for a product made in the morning and sold at night, which is why the two operations sit within arm's reach of each other.
The batter itself is time-sensitive
Jalebi batter is fermented, which loosens it and produces the faint sourness that offsets the syrup. Fermentation continues in the bowl and changes the batter hour by hour.
Vendors mix in fresh batter through the day to hold the consistency steady, judging by how the stream falls from the piping cloth rather than by any measurement.
Frying in view is also a claim about the fat
Repeatedly heated frying fat degrades, and the change shows in its color and its smell. A customer watching the pan can see what state the oil is in.
Vendors who fry in the open are making that visible deliberately. It is a quality signal that a sealed package has no way of offering.
The format shapes how it is portioned and sold
Because the product cannot be stocked, it is made in small runs sized to the queue standing in front of the pan, and sold by weight straight off the drainage rack.
That is why jalebi appears in the morning and again around evening tea rather than continuously, and why a stall that has stopped frying has genuinely stopped selling it.