CHECK FOR THE FOLLOWING:
Are there any penetrations above the opening that could be the source of leaks like a wall vent or louver for attic circulation?
Look for cracks in the stucco above openings. Route out all cracks should be with a grinder and caulk. Elastomeric paint may also be a solution but not in all cases.
Broken, clogged or leaking gutters and roof flashing may excessively funnel rain water over doors and windows.
Check siding trim for faulty old or cracked caulking. There are many grades of caulking and most do not last forever. 100% silicone is not affected by the sun’s degrading UV rays which will not affect 100% silicone.
Windows and doors should have flashing installed before siding as an added protection rather than relying solely on the trim to divert water.
See if the door is installed in a recess lower than the finish floor? Check to see if the recess sloped outwards correctly or incorrectly inwards?
Look for negative pitched concrete slabs and decking that funnel water under and around thresholds and jambs. You should not rely on caulking as the sole defense in these areas. Caulking typically fails here in time.
Links to Useful Articles:
2) “Installing an Exterior Door”, Journal of Light Construction by John Spier May 29, 2019.