purple hair dye

so about a month ago I dyed my hair purple with splat because I feel like it’s the only hair dye that stays in my hair for long periods of time, but it’s basically gone now. I’ve tried other purple hair dyes and they don’t stay for long either, so is it that purple just isn’t a color that lasts long or is it something to do with my hair? ( because I have a feeling it is lol). I have light brown hair and I usually don’t bleach when putting on hair dye because I don’t want to completely kill my hair, and I shower with hot water usually so that probably has something to do with it not lasting. but what’s confusing me is that splat usually stays in for AGES when I do these exact same things so that’s why I think it’s the color, but if not please correct me! I’m just genuinely curious and want to know if anyone on here knows :-)