At my previous company, the lifetime projected volume of the ASIC we were designing was around 50,000 units. Yet, the ASIC vendor had to provide significant complex IP and especially engineering headcount to shepherd the chip to the prototype stage. Unfortunately, the market changed and that chip never made it to production. Sorry, ASIC vendor!
No wonder that most ASIC vendors are having a very tough life, with rising costs and declining design starts (and especially, fewer designs going to mass production). Contrast this with foundries such as TSMC, which get the customer to do all the IP integration, implementation, and verification, and the foundry can just focus on selling wafers. No wonder this model is eclipsing the ASIC model.