It's because abortion is a medical procedure and is mostly safe. If he goes through the legal way, the alpha would be informed and he will become an actual participant of getting rid of the baby. If through illegal way, alpha would probably live his whole life without knowing anything. Meanwhile, a miscarriage due to fucking is not only more painful and dangerous to his body but would mean that the alpha would discover he is pregnant and that he unknowingly killed the baby coz he was horny, so of course it would be bad, really bad.

'I want abortion, but early miscarriage would be bad.' MC, who is clearly a schizo.
WTF, who thinks like this? Who writes this? Moscareto, you are better than this shit, what happened, did you rot your brain to the core with too much porn?