You are blaming the wrong company. Qualcomm is the company that makes it hard to do alternative software platforms for mobile. Even apple still licenses their solutions (they are working on their own modem but have not shipped that yet). The issue is to get your hardware + software solution certified for use on mobile networks. That's very hard and it's not a very fair game. It requires a nod of approval from operators and intellectual property from Qualcomm.
Apple simply plays the FOMO factor. They do deals with operators. And the deal is typically "take it or leave it and watch your customers jump to your competitors". When they first did that, a few operators were smart enough to say yes. The rest has since learned to do as Apple says. But even so, Apple pays the Qualcomm tax.
The rest of the phone industry plays this game by just sharing a lot of components (Google's Android, Qualcomm's hardware, Samsung screens, Sony camera sensors, etc.). Google has tried to get into that market directly by buying Motorola at some point and by doing their Nexus and Pixel phones. But they never really became a dominant manufacturer. Google is a supplier of mostly software in this space.
Out of all that stuff, Qualcomm is the one that has the keys to the ecosystem. You need 4G/5G compatibility, which they provide via their hardware and software. And you need to get your solution certified. Without that you have an interesting device that does not talk to a mobile network. Even if you manage to build your own version of that (which is hard, but e.g. Apple is doing it), you still need to get it certified and then after you succeed with that, you need to license a lot of patents from Qualcomm to actually ship it. The price of entry to the market is very high. Long story short, there are not a lot of alternatives in the market and a few that have issues being allowed in mainstream markets like the US for IP licensing reasons.