It's less common for limited data like you have, it's more common for unlimited data. Essentially they don't want people using tethering as a replacement for home internet on these plans
I could have got an unlimited plan, except that it costs more and even with tethering I don't go through more than 40GB so I saved a bit and downgraded to a limited plan. The data limitations was a personal choice.
I don't see any of the providers here in the UK with different amounts for tethering Vs data.
My 60Gb can be consumed by YouTube, HN or tethering. It doesn't really matter to them.
Is this common in other countries?