It's about being prepared for all kinds of eventualities, whatever they might be.
For example, last year and early this year heavy winds fell trees on electric lines both in Finland and Sweden, cutting off electricity locally for many days. There was a pandemic not too long ago. Waterworks problems have happened in the past in Finland and also happened this year in Sweden. DDoSing happens here and there, it can impact banks and such.
In addition, grayzone/hybrid operations i.e. all kinds of stupid bullying are constantly conducted: for example, earlier today a submarine cable between Germany and Finland (C-Lion1) was cut, and later today another submarine cable between Lithuania and Sweden was cut as well. Such cables don't just snap by themselves.
Like the Finnish page says: "Prepared people cope better".
https://www.suomi.fi/guides/preparedness
https://www.msb.se/en/advice-for-individuals/the-brochure-in...
Your general points are valid, but undersea cables do fail for many reasons. A few moments of googling turns up industry failure statistics. Most are still due to human activity in some way (but unintentional, like an anchor drag) but plenty are due to the natural environment of the sea floor.