Why have a femorsl endarterectomy when there are atherectomy procedures to consider instead?

It's just an option. Vascular surgeons and their patients are often presented with a complex series of choices and operative approaches. There are always different approaches that can be taken. This includes minimally invasive techniques, open surgery, or hybrid approaches that combined both. I use the approach you mention when patients do not have any vein for a bypass and have pain at rest. Can be effective.
Good Question! Sfa treatment is usually by bypass or interventions (atherectomy or angioplasty/stenting) for long total occlusions and re-blockages of previous stents and atherecomy, surgery may be better, but as initial treatment, atherectomy and or balloon and stent is a reasonable choice, even in total occlusions if they can be probed and passed, or steered around using newer endovascular techniques.