Can someone please explain to me why in Switzerland they don't just tax share dealing as income? Seems weird that it's either not taxed for small personal gains, or subject to Capital Gains Tax for a whopping 50% if you go over their line to be classed as a business. Why can't they just make it simpler and count it as overall earnings?

Many countries don't as they usually have to allow losses to be carried forward. Also as you can choose when to sell & also close out other losses. The UK used not to tax capital gains, they give an 11k annual limit & have allowed PEPS / ISA's to be tax free. Plenty of people will have accumulated over £1,000,000 in such schemes over the last 30 years.

Edit, remember CH has always been a huge tax haven for the worlds wealthiest individuals. Numbered accounts, tax evasion being legal benefited CH over the last 80 years.