Why does a backup not backup your photos?

Last night, I purchased a brand new iPhone 15 at T-Mobile and traded in my old iPhone Xr. My old phone had automatically performed a backup the day before so I thought I was ready to transfer my data to my new phone. After getting home and transferring my data, I realized that none of my old photos and videos transferred to my new phone. The reason this happened is because for whatever reason, Apple thought it was good idea to make it to where you have to enable a setting to include your photos in a backup. I was not aware of this because I assumed, probably like most people, that they would automatically be included in the backup. After realizing this, I went back to T-mobile the following morning to see if I could get my old photos back and found that my old phone had already been wiped and there was nothing I could do to get them back. So my first question is, why the **** are personal photos and videos not automatically backed up when a backup is performed? Everything else on my phone was backed up including progress I had made in games that were on my phone. How my progress in a VIDEO GAME backed up but not the thing that most people would probably consider the most important thing on their phone. And if possible, how do I get my old photos back? I lost 5 years worth of photos from family vacations and time spent with friends all because someone at Apple thought it would be a good idea to make it to where you have to enable a setting for photos to be included in a backup. If anyone reads this, which I doubt anyone will, make sure that if you purchase a new iPhone, and decide to transfer your data the same way I did that the setting to backup your photos is enabled. Otherwise you will lose them all. This experience has severely worsened my already unfavorably view of Apple and I can guarantee I WILL NOT be buying any other Apple products anytime soon and possibly ever again. I’ll also be sure to let everyone else I know hear about and encourage not to buy from Apple either.