We only report windshear on the ATIS and the tower advise the approaching aircraft the extent of the windshear determined from reports by landing crews.
Windshear is dynamic and as such one crew might get +15kts, the next might just say its a bit bumpy, the next might get -10kts, so if we changed the atis after every report to reflect the severity of the shear then the atis letter is going to change every 2 mins which means tha the poor sods who briefed themseles inboud with Alpha, suddenly get told that the information is Zulu and then have to get that and re-brief based on information which will no doubt have changed by the time they have completed the re-brief