Because this is literally about the time-domain solution to heat conduction and fluid dynamics (convention) with different initial conditions and boundary conditions (shape of vessel, temperatures at boundaries, etc.).
For example if there isn't uniformity of initial temperature, if there isn't uniformed of the applied cold sink, if there isn't uniformity of heat flux capacity due to conductivity of the interfacing boundary conditions, etc. There's even questions about the water purity or contaminants which definitely would change the answer.
These are not and often can not be controlled. And in practice at home, you will never duplicate even what the answer is in a control lab experiment.
It is the norm to have a range solutions that entirely depend upon initial conditions and boundary conditions. And there's also uncertainty of even knowing the values of these conditions.
Expecting a simplistic yes/no answer to many problems ESPECIALLY those involving heat transfer and fluid dynamics is like asking for a specific date for your date from your date of birth or your childhood medical history.
See also climate change - we DO NOT KNOW there is a specific date when things "tip" and ANYONE claiming there is a date let alone timeframe is a liar or so ignorant they can't possibly be right! The error of any model is larger than the estimate value itself.
You'd think people would have learned something from the 20th century about the FACT that we do not live in a 19th clock-work universe with complete predictability. We know how it can never be predictable especially if fluid dynamics is involved - you know, mathematical chaos and all.