I'm not sure it's easy for a software engineer to develop a model, it's quite an orthogonal skill, you need a solid grasp on mathematics and especially statistics.
It's not easy, but there are capable developers that are proficient in data science and it may be cost effective to hire one such (high cost) programmer than one (average cost) data-scientist and another (average cost) programmer.
True, but those software engineers exist, and FAANG and FAANG-adjacent companies offer the work opportunities, prestige and salaries to attract those "twofer" engineers.