Premium Bonds are a good tax free investment. I made £375 on £10000 last year. I would have needed to make 6.25% on a taxed investment to better that.
I maxed out to £50000 in June and have already made £250.
Partly because you were lucky mind. The average expected return rate on £10k would be £325 on the current prize payout rate (which is decreasing in just over 3 weeks time).
To be better off with Premium Bonds than paying the tax above the personal savings allowance means being a higher or additional rate tax payer, which most people aren't. It also really means having exceeded £20k ISA allowance, as the interest rates on even the top cash ISA (let alone a sensible S&S ISA choice) is significantly higher than the average Premium Bonds payout rate. And on top of that you'd need to have exceeded your personal savings allowance, which for additional rate tax payers is £0, but for higher rates taxpayer's is £500, which means having around £10-15k of taxed savings, on top of £20k a year in ISAs. 93% of ISA holders don't max them out, so it's a small minority position.
Basically, it's a very privileged position to be in - Premium Bonds are not better than cash savings for all but a tiny number of very well off taxpayers.
I hold Premium Bonds mainly because I like the idea of doing a lottery where I get to keep my stake. It's most certainly not paying me more than other savings and investments though, even after tax implications.
Also while they may be useful as a short-term savings measure, or those very risk-averse, for any long term investment, even the median 3.3% return rate (decreasing in August) is a very poor level of growth for a medium or long term investment.
Edit to add - politically, the government will want to promote Premium Bonds regardless of cash ISA changes, because the government run the Premium Bonds, so we're effectively lending the government our money, which isn't really true in cash ISAs.