Because it’s not up to anyone else to decide on Inyanei Shamayim.
Because the fact that a person may receive Olam Haba for dying al kidush Hashem does not mean you need to be the one to do it – that’s up to Hashgacha Pratit. Our job is to SAVE another Jew’s life when in danger, and CERTAINLY to prevent their suffering. Allowing the contrary to occur is tantamount to murdering them ch”v.
Should I go on a rampage chalila telling non religious Jews to keep Shabbos or else I’ll kill them, and actually do so (again, ch”v), in order to get them their olam haba?
It’s very similar to what you’re describing…
Every Jew has their own challenge(s) on this Earth in fulfilling their duty to bring G-d’s name glory through creating a Dira Besachtonim. It is not up to us to judge or decide for another Jew where their challenge lies. I’m certain there are mitzvos that you find very hard to do yourself – while many very non Frum Yidden may very well find it extremely easy and simple to do others which you may never have even thought about – like Tzdaka and Ahavas Yisrael. So their challenge is to keep Shabbos while yours is to think more positively of your fellow Jew! To see and decide that their being non Shabbos keeping and not davening on a daily basis as a basis for the opinion that their only “salvation” (sounds Xtian doesn’t it?) is to die al kidush Hashem is a bit twisted, and I would recommend for you to look very deep into your priorities and moral perspective in the light of the Torah to get it reoriented a bit….
I don’t mean it in a scathing, heated sense! Just a very sincere recommendation!!