I feel like InfluxDB were the best time series database in town for some time (2015-2018?), but they failed to monetise and exploit the space properly, and now they have lots of competition, many of it better in a lot of cases ( e.g. speed, space use, ease of use, pricing, integrations), be it for self-hosted or cloud.

Some of it was wasted effort ( Cheonograf is still useless compared to Grafana, who thought it's a good idea to compete with it?), some was poor luck, some was decisions that backfired ( like removing clustering from the free version). Some of it was everyone deciding pull is better than push ( i disagree in most cases, but see the point).

Telegraf still remains a very solid collecting agent and IMHO the best in class. With everyone (from the SaaS monitoring vendors ) moving to OpenTelemetry i think that in some time it'll fall behind as well.