To put it into context, a junior doctor in the UK makes £29,384, and they will leave university with close to 6 figure debt, with 7.3% interest rates.
But it's not even just that. Over the last few years, the UK has embraced the roles of non-medically trained physician associates (PA), which in the USA have been a success by relieving medically trained doctors from the more protocolisable jobs, so they can focus on the more difficult. However, a PA earns £39,766.76 - far more than the juniors with none of the responsibility. I won't go into details on the issues about how juniors have to maintain annual portfolios, change hospitals every year etc. etc., because the Royal Colleges say it's necessary to become a good doctor, whereas PAs don't need to do any of it.
So when juniors in the UK see this, that they could have gone to University for 2 years rather than 5, with lower entrance requirements, and end up in a far better financial situation in a shorter time, many of them just don't want to be a doctor anymore.
I can say, without a doubt, that junior doctors will strike in the UK within the next 2 years. I am no longer one, but I completely get where they are coming from, and support them.