I am involved in a sport well removed from Pro Cycing and on occasion spend time sitting with our commentators. They start commentating at around 10am and are often still at it at9pm or later they have no script, just their notes sometimes 40 or 50 page folders, so even finding the fact relevant to the situation thousands are watching at a moments notice is a work of wonder quite how they manage to keep people entertained is still after 40 years plus a complete mystery to me.
To those out there who seem to think all commentators are "rubbish" and do nothing but spew "babble", I say, do what I did and try in the privacy of your own home! See just how long you can hold a commentary that will not only inform cyclings equivalent of avid trainspotters who know how deep the flange is on a waggon wheel, but to engage the people who with almost no knowledge of cycling its rules regs let alone who the participants are and might well be watching for the first time and see how long you last my best is 10 minutes and no one with half a brain would pay me a cent. As the Poles say "Its easy to stink with full trousers"!!!!!!!
For some people it's incredibly hard, others are complete naturals in speaking, speaking, speaking...
Another point is that you usually don't have to commentate cycling on your own - it's usually two commentators, at German Eurosport there are 4 people at the moment for the Giro, for the big races they often have 1 commentator who leads the conversation, two experts who explain, chat, give their expectations and assessments, and one person who points out the "cultural highlights", often translates the interviews (and also cares about social media).
So you cannot just get lost in your monologue, that might be more difficult for some, but it's not like you have to be a single entertainer for hours... Even if it's just two people they can have a conversation. Discuss, ask the other one questions, take a break... I think that should make things much easier, since you have some input and are not in this vaccuum where you don't know what anyone else would say or see in this moment.