There are exactly 0 jobs for undergrad BSc in most countries, especially if you want any kind of liveable salary and not be a pipetting robot.
Most interesting jobs require at least a PhD, and these requirements are usually firm - there is a glut of applicants, employers can save some work by deleting those who don't fulfill the requirements and still get good people. You can't get postdocs without a PhD (from my experience, in >95% of cases), and a postdoc is the 'prescribed' way towards a Prof. If you are trying to come in mid-career from a non-academic background, you don't have the papers, you don't have the grants, you're a hiring risk.
The system itself makes careerists, it only very rarely allows outsiders coming in.