Tax is too complicated, so much room for improvement

Why rebates? Why can't we directly cancel it? Why gst + extra tax on stock exchange? Why different tax for long term and short term investments? Why tax on critical medical expenses? Why extreme tax on vehicle purchase? Why don't we have + tax scheme (example you earn 12.75pa you get a bonus of 25k why cant government just tax extra on this 25k like having a buffer transmission zone it seems so unfair just for that extra 25k that too bonus you have to enter the complete tax return of 13lpa)

(Not against the new tax scheme just frustrated on how complicated it is. With zero consistency)