Hm, http://stats.research.icann.org/dns/tld_report/ tells you that the zone is signed (search for
Your registrar needs add DNSSEC support for the ch zone. I’m not sure but I think only only a small number of registrars have added support for the ch. TLD (top level domain). I don’t think there is a technical reason but I would ask you registrar. Cloudflare doesn’t care which TLD DNSSEC is enabled for, it just signs the zone.
DNSSEC Adoption has been very slow, for example NameCheap only supports 14 TLDs out of the 1392 (from the 1st link as of 2018-09-22 00:02:08): https://www.namecheap.com/support/Help Center/article.aspx/9718/2232/nameservers-and-tlds-supportedunsupported-by-dnssec
Some stats on the number of signed domains in the ch. zone: https://www.nic.ch/statistics/dnssec/