I'm not convinced it's the Gove reforms. I think it's much more likely to be the constant message that STEM subjects are the ones that are important, that help you get a better (and better paid) job. I don't know whether that is true or not, but it is the message that young people are being given.
If more people do STEM subjects, and biology and chemistry entries are both up by 9%, something is going to have to give. I don't think it's a bad thing that more people are doing 3 A levels rather than 4. My children's school never allowed more than 3, except where further maths was the 4th, on the grounds that quality was better than quantity and no universities ask for 4.
I'm absolutely not anti-English. I did English A level 40 years ago, both my children did it, and my husband and 2 sisters did English degrees. But I can see why people are moving away from it. I think many people who might previously have done English (or music, art, drama, film studies etc) may be getting the impression that those subjects are 'luxuries' and that they should study STEM subjects and read, make music, paint, act, etc as a hobby.
Incidentally, the most prolific young reader I know wanted to do A level English as a 5th A level, but was persuaded by her school, sensibly I think, not to. She did maths, further maths, biology and chemistry and is now studying chemistry but continuing to read a huge amount for pleasure.