To be clear, Flightradar24 and other ADS-B-based online services do not provide enough data to come to a meaningful conclusion about these kinds of accident. The resolution is often too coarse to even see how quickly a plane would've pitched down, assuming it did so quickly.
Online services actually do have the data available, just their online graphing is a smoothed out version of the data.
Generally data is received every 5 seconds. In cases such as Lion Air, they downloaded all the granular data from nearby receivers and provided some analysis in their blog.
They also made available the raw data for the public to download:
This data is actually gathered by hobbyist and you can be a part of their network all it costs is about $25 for an ADS-B USB adapter. https://www.flightradar24.com/build-your-own
They also offer free membership (499/yr) if you share data.
Every flight broadcasts this data kinda like GPS and all you need is an antenna to receive it. In fact the tracking is basically done via ground-based GPS(ADS-B) by measuring the time delays between different receivers in the vicinity. The problem is that there aren't many hobbyists in those parts of Africa so coverage is sparse. In America, its pretty spot on in most locations. A USB adapter can surprisingly pick up planes as far away as 400 miles.
E.g. you can get an SDR with built-in ADS-B specific low-noise amplifier and SAW filter also for $25. (This can't do general purpose stuff though, unlike the one linked by parent.) Or you can get their general-purpose SDR and their broadband LNA for $40 total.
