If I was HR and I had a choice between a Javascript developer for 50k with a clean record and a Javascript developer with a 5 year old conviction for 40k - I'd actually pick the later. But only if I could fire him immediately if he turns out to actually be a cookie monster.
That's how HR acts in practice though. Especially with automated tools, checking off a "have you ever had a prior conviction" box just gets you an automated rejection without a human ever looking at it
Yes a lot of companies do. Especially minimum wage jobs. Because there are vastly more people without a record willing to work. But now imagine you have a previous conviction but you are willing to work for less than minimum wage?
If I value a fry cook for $10 an hour and I get 1 person with a previous conviction who wants to work for $5 - I'll hire him in a heartbeat so long as I could fire him at any moment. And since I'm a good employer I'll make him a deal to pay him $10 an hour after 6 months provided he stays clean and works hard.
As it stands I'm not allowed to do any of that - so the convict remains unemployed and will probably commit more crime just to survive.
That's just going to make a space underclass. There's not a benefit to convicting people because hey, cheap labor. The same forces are already happening with prison labor.
What you are suggesting is that any single mistake is now a permanent albatross around a person's neck and a reason for them to be permanently deprived. In a society where we have so many laws that everyone breaks several a day, this just leads to selective enforcement and corruption.