Why do Montgomery Escalator Chains stretch

Stretching chains are not brand specific. All chains strech to some degree, escalator chains, timing chains, bicycle chains. Lubrication is essential to extended life. Environment , proper indexing, track alignment, chain tension has an impact on how a chain wears. Also the steel used to manufacture the chains is different than it was 30 years ago. Much of it is made from recycled steel. Its is unknown if that effects the wear rate. If the wear is skewing the indexing of the steps it may be time to replace the chains. If the wear is slight or not exceeding code for minimum gap (step to step) you may be able to prolong the life of the chains by LUBRICATION. I have heard of Montgomery step chains which are approaching 30 years in age with very little sign of wear.