No, like any startup they needed to launch an MVP and iterate. Waiting until everything is available on every platform only makes sense if you have the time and resources, which they didn't. They were a small team with limited resources.
Clubhouse wasn’t explosively popular when it launched. The success came a few months later, at which point they had more people seeking invites than they wanted to allow on to the platform. Focusing on getting something minimal out the door and scaling it up is the right choice.
If you’re going to pick one platform to launch an MVP, iOS is almost always the right choice. Tech enthusiasts and early adopters skew toward iOS by a small margin and iOS is a more predictable platform to develop for because you can count on most of your user base being on the current iOS version. Android is a development minefield by comparison, especially when it comes to audio and video.