Airlines lose bags. That’s just a fact of life. If you fly enough, and check a bag, eventually the statistics will catch up with you.
Now to be fair, most of the time airlines don’t actually lose your bag, they just misplace it for awhile. It ends up on the wrong plane, sits in baggage purgatory, or whatever. That is to say most of the time you’ll eventually be reunited with it. Even so, it can be kind of annoying in the interim to not have your stuff.
Most airlines recognize this and have some form of distressed passenger amenity kit that they offer to passengers who have had their bag get lost. The contents of these kits tends to vary, however, as airlines seem to have different concepts of what is “essential.”