Why do people avoid discussing sad topics with me?

For just one example, happened a while ago, but a really good example. A few friends and i were discussing some sad topics. One of them said that their mom had mental illness which of course is really sad. Everyone in the group was really sympathetic and said how sorry they were. Then it somehow got around to me saying my mom had died from cancer when I was 12 as the topics was moms so I just had to reveal it. They all just said they were sorry and changed the topic. Now they discuss other stuff with me no problem. I’ve also unfortunately been diagnosed with melanoma recently at 28 and of course many of my close people are really upset but acquaintances some are upset but others it’s like they don’t care less because they just sound emotionless and say their apologies and then change the topic. Same attitude from some doctors. Almost seems they imply I’m being over the top about feeling sad about it or others are just distant and cold and try to figure out how I got it. Don’t know whether this is interest or whether they are implying I brought it on myself. Anyway sorry I’m going on a bit

Why do people avoid discussing sad topics with me?
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