Your existing bike hopefully fits you great rather than having to modify a low-mid grade ebike. Perhaps you don't have space for more bikes. Perhaps you want a bike made of good components that are easy to repair. It's a significant amount of money but there are absolutely reasons.

I have a ebike that cost ~1500 in 2018 and is probably comparable to what $2k would buy you these days. It's very heavy and while the drivetrain is repairable, there are important pieces of it that I would struggle to repair/replace if they died today.

I have a steel touring bike that's significantly lighter, has standard sized parts that can be repaired, replaced and upgraded (many of which I have already upgraded in the last 15 years) and fits me like a glove. If I didn't own an ebike and you asked me whether I'd rather spend $2k buying something like my ebike or adding a 750W motor to my Surly, I'd upgrade my touring bike.