Tubes wear out. They do not last forever.
You'd be surprised by how long they do last. 75% of the time tubes do not need to be changed when someone changes them. They can indeed last for 20yrs or more. Of course this depends on what tube it is and a number of other factors that I'm not going to get into. But the typical people change tubes around the 5yr mark. I take their old tubes and use them.
In comparison many people use a car till around 100,000 miles let's say, well these tubes being swapped at 5yr mark is about 10,000 miles on your car saying it should be junked. Well maybe not that much but you get the idea. Tubes last for a long time if their quality stuff, and taken care of. But if let's say you live in Chicago, and it's winter, and the amps been sitting in your car trunk all day cause you got a gig that night, and have to cruise to show right after work. So you get to the show plug in your gear and turn it on before it's had a chance to warm up to room temp naturally. Well that's gonna put a lot of stress on your tube, which will make it burn out faster. That's just one way of ruining your tubes mind you, but you get my gums flapping.
Now if you just don't like tubes..hey everyone likes different shite, to each their own. I will say that Solid State is cleaner that tubes so on the lows you get more fidelity, well and all around, and that by putting a tube pre in their you can have both to a certain degree.
But don't be kidding yourself when a chick tells you it's not about size, she's just being nice! It's always about size! Bigger is always better! And that my friends is a fact! Well most of the time, I'm hung like a 5yr old so.....hahahaha
If you don't wanna lug around a 100lb, 2000$ head then stick with the 5lb chepo heads, as long as they work for you.
Still Aguilar makes the 751 head and it's one of my favorite heads ever, (have heard many you probably have never heard of, not all by any means, just a reference)and it's about 50lbs with just 3 tubes in the preamps stage. So it ain't super light by any means. But it sounds amazing! One of the best instances of blending the 2 technologies together imo. But opinions are like as*holes, everyone's get one....

Now for me I ,obviously from my above post, have never found a light amp that sounds better than a heavy amp! Whether it's all tube, or a hybrid they're gonna be heavy and big. Don't get me wrong I hate lugging around my 80lb Accugroove El Whappo, and my 70lb Fender SuperBassman, but I'm a tone slut. I just can't find any combo or small rig that can at least passably sound decent! The less speakers you have the less air you move, the smaller your transformers the thinner your sound. It's just physics really. Really wish TV manufacturers would figure this out. Rather have a 100lb tv, than a 1lb tv that I can't freaking hear! Micro this and micro that...it's so annoying. And I'd rather have a 2lb phone than a 1/16th of a pound phone that I can't freaking hear! Oh btw get some good earplugs! Earasers are super comfortable, way more than the Eytomic Research ones.