What lazide saying is that some important information is stored at the end (as in the very end of the book/movie or at the end of the line). So imagine there is a 1TB .zip archive in the tape, the tape device have to go further (deeper) into that 1TB file to get that last bit of vital data that the user want to see. Normally the vital bit usually at the start of the file (as in the front line/beginning of the book) that the user have the information ready before they could transfer it. But for lazide case, the tape device have to keep reading the entire 1TB zip to get that last vital bit of information which made it slow. It is more like it cannot "skip the line" and would have to go through entire line to get there.

They do - it’s very slow, and entirely linear. It also puts wear on the tape, so if you do it a lot you’ll break the tape in a not-super-long-time.

And since you wouldn’t know where the end is by reading the beginning, you’ll have to keep reading until you hit the right marker - and seek backwards (which you generally can’t read backwards on most tape drives, so you need to jump back and re-read).