You're not the only one Voo. I don't and won't pay my kids for getting good grades. The reward they will get for their good grades is the chance to do anything they want post school. If hard to get into university courses are what they want, it will be offered to them. If an apprenticeship is what they are after, then their grades will put them above the other candidates...assuming they put in the work to get those grades now.
My daughter is a bit of a swot and at 14 is getting teased by the other kids at school who think it's 'nerdish' to do well. To them she says 'think/say what you like, one day you'll be working for ME'.