There is no such thing as DNS propagation, only DNS cache invalidation, and by polling it, you are making your old records stay in more caches and for longer.
You're right, it's TTL not LRU. The authoritative server publishes a TTL with the record — "you may keep this for N seconds" — and when it's up the resolver has to ask again no matter how popular it is.
LRU does show up in resolvers, but as memory management: cache is full, evict the least recently used early. It can only make something disappear sooner than its TTL, never later.
It's time-based because there's no back-channel. An authoritative server has no idea who's holding a copy of its records, so it can't push an invalidation.
BGP, on the other hand, propagates.