Am i missing something or does it seem a bit silly compared to running a 1.5 inch headtube (or is it 44mm now?) that can run all the forks on the market and suitable for various anglesets etc.

what benefits do they have?

The benefits of an oversized lower bearing with the ability to choose from the wider range of ‘normal’ sized stems.

but why not have a larger upper bearing as well?

Its because not many people bought into full 1.5” tubes because the most of the stems on the market are
1 1/8”

I suppose sometimes it just comes down to looks. A 44mm headtube with a reducer headset and ‘normal’ stem just doesn’t look as ‘right’ as with a tapered headtube.

wishiwascalledsteve and fourcrossjohn, 1.5 head tubes don’t stop you using a tapered or even 1 1/8th fork and stem if you so choose.

OP I don’t understand what disadvantages straight 1.5 head tubes have either.

what benefits do they have?

For you? None that you’d notice.

For bike companies? Makes the latest product year look different from the last and justifes x hundred quid price increase. May just fool muppets into thinking they need to upgrade.

Or am I being cynical?

OP I don’t understand what disadvantages straight 1.5 head tubes have either.

weight.

head tube weight
headset weight.

head tube weight

seriously? must be 5g and a couple of extra ball bearings which is nothing for your average MTBer. Countering that you have increased stiffness allowing thinner walls. Also, a 1.5 straight tube will be cheaper to produce than a tapered version and the extra money could be used for better materials or better engineered dropouts to regain that weight lost…

Positives of a 1.5 straight are increased stiffness, a greater choice of forks and stems, smoother headsets and/or a great range from an angleset.

Let’s be honest about this.

The ONLY reason why anything other than 1 1/8th straight is now so popular is because everyone is retrofitting Cane Creek angle reducer sets and the manufacturers are able to provide the same future proofing of geometry in the same way.

I’m 105kg and I can’t tell the difference between 1.5″, 1/18th and tapered head tube. Undoubtedly my next bike will have one either because I will want to fit the CC angle set or because I won’t have any choice.