Apple’s estimated delivery dates are usually very accurate. Some iPad models are in short supply in some geographic regions, while other models may be immediately available. If you need your iPad quickly, perhaps consider a model with more internal storage - or less - as delivery time may be considerably shorter.
The entire electronics industry is struggling with manufacture and availability of semiconductors. Similarly, there are global shipping delays affecting all commodities. Combined, these two factors alone are significantly impacting availability of goods worldwide.