I can see abortion being a State issue, but there's no Federal law against murder. Not all crimes need to be addressed at the Federal level.
There should be no need to have federal laws against abortion, as the states should give legal protection against slaughter to unborn people within their jurisdiction.
The problem is that sometimes state governments refuse to provide legal protection to people they disfavor. This is why the 14th Amendment was written... some Democrat-controlled governments were allowing black people to be disarmed, whipped, killed, disenfranchised and so on. The 14th allows the federal government to step in and protect rights of groups of people when the state government refuses to do so.
So if a state legalizes killing Chinese, the federal government is authorized to prevent the murder of Chinese people in that state with legislation. It is the same with children before birth.