want to watch blu-ray movies on my Imac but Apple has no blu-ray player why?

There is having the compatible Blu-ray hardware, and then the third-party software that will play that content. VLC will not play Blu-ray content, but MacGO's Blu-ray Player Standard will play Blu-ray and DVD content with a watermark until you are ready to pay for it. It will not play any 4K or UltraHD Blu-ray media. It is also 32-bit software. The Blu-ray Player Pro can apparently play 4K media, but I don't have the player to support or test that format.

How about any of these?

https://www.amazon.com/s/?ie=UTF8&keywords=blue+ray+player+for+mac&tag=mh0b-20&index=aps&hvadid=78408976434657&hvqmt=e&hvbmt=be&hvdev=c&ref=pd_sl_5zge9ee5lh_e

Apple has never supported Blue-Ray, however if you would like you can contact OWC (www.macsales.com) where they have complete Blue Ray solutions for Mac users. If you are in North American you can call them or if you are not, you can do chats and they can help steer you to a solution that will fit your needs.