https://thenextweb.com/syndication/2019/03/26/boeing-737-maxs-crashes-explained-by-an-aircraft-expert/

The Boeing 737 is the most produced commercial airplane in history: over 10,000 have been built since it first flew in 1967, with thousands more on order. Even the UK’s Royal Air Force is to put them into service as the P8a Poseidon.

An airplane which flies that much will have accidents. The 737 has had over 200 that have led to the loss of the airplane, resulting in over 5,000 fatalities over its 51 years.