Humans will have babies every 1-2 years consistently if fertile with unprotected intercourse. Are you saying homo erectus is that different?

I don't believe it, we're no different from hunter gatherers in capability of having yearly offspring. In religious communities where I grew up, most families had kids spaced ~2 years apart, and they had access to birth control. Nursing hormones don't outright block pregnancy for 4 years. I bet we can find a study

edit: from the NHS "Most couples will get pregnant within a year if they have regular sex and don't use contraception". We can safely assume this applies to hunter gatherers. This 4 year thing is absurd.

This has to be due to infant mortality. I can't imagine they weren't just having sex and getting pregnant whenever they could

This is called "convergent evolution" where two unrelated species develop to look the same due to similar needs