Why do tech companies even do this? Why can't everyone just agree on a standard and stick with it from the start instead of having a war that means us consumers who buy gear from the wrong side will suffer.
There's millions of reasons...
Waiting for an agreed standard is no good, because that takes forever. And most standards just merge together a few of the most popular proprietary methods and call it a standard, so you can't just start on step 2 in any case.
Adopting whatever came along first is no good, because what comes later might have higher requirements and crippling yourself to the older one gives you little or no benefit.
It can be slow and expensive to design something that makes everybody happy. Sometimes you have to do what's best, right now, for your product.
It's often less expensive to start simple and proprietary, then convert and adapt later, when something better comes along, or once it eventually becomes competitively priced.
Companies don't want to spend all their time and money designing and developing infrastructure, only to have some cheaper imitator with the 2nd mover advantage come along and undercut them and be able to use their work without effort.
Companies only need a big enough market to develop economies of scale. Making their market larger than necessary to do that offers them no extra benefits.
And that's just scratching the surface.