The stall speed for a Learjet-55 is approximately 110 knots at a typical operating weight, depending on configuration and environmental factors.

The last speed reading of the Jet in Philly was 241 Kph.

How many passengers can the jet handle?
A Learjet 55 typically accommodates between 7 and 8 passengers comfortably, though some configurations may allow for up to 10 passengers in a high-density seating arrangement.

There were 5 adults and one child on board the jet, with minimum luggage.

They say the full fuel tanks and the balance of the people on board can affect control of the aircraft. However, there wasn't a high amount of passengers, there was a low altitude, dense air, no wind and no rapid increase of altitude climbing taking place.

Also, the sound of the engines roaring could be heard as it dropped like a missile from the sky, which rules out engine failure.
It also rules out contaminated fuel.

Something catastrophic happened to the aircraft shortly after take off that eliminated any correction by the pilots.

This aircraft was manufactured around 1981, that is apx 43 years old. Any number of inspections in Mexico could have been lax to allow this older jet to continue flying.

There are metal fatigue issues and numerous mechanical issues that would cause this sudden crash.
It is possible that a total hydraulic system failure could have taken place.
It could have been hit by a drone, or had hi-tech electronic weapon systems used against it.
It could have been hit by a shoulder fired missile.
It could have been disabled in any number of areas with an on board bomb that went off.

My best guess is it was an on board bomb.
My second guess would be a mechanical failure that was so catastrophic that the pilots would not be able to fly the plane to recover.
My third guess would be a hit by a drone, or an attack by a drone that caused the sudden crash. There are simply too many coincidences involving drone sightings to dismiss that possibility.

There is also a strong possibility this was a drug cartel hit on a competitive cartel where these jets are used to traffic drugs at times. Hiding nefarious drug running using medevac jets is a very clever way to run drugs around the world.

Unfortunately we may never know the full truth. Our government system is corrupt and those that make $ billions in drug running and child trafficking cover all their bases to prevent being arrested.
George Eaton