Why changes of state are considered physical transition and not chemical processes

In a physical change, the chemical compontents are not altered. If ice melts into a liquid it's still water regardless; same goes if it were to vaporize and turn into a gas.

In a chemical change, the chemical components are altered. If you left a metal outside after it rained it would rust which would be a chemical process since it is chemically altered. Flamability is also a chemical process.