This is not entirely true I'm afraid. During 60 years of crewed spaceflight a number of spacesuits for different uses have been developed. All different and specifically taylored (literally...) for the task. There are the "simple but quite comfortable" pressure suits that are worn inside a spacecraft during critical phases of the mission. Their main task is to offer protection against depressurisation. They have no life-support of their own and no cooling.
Then there are EVA suits for "free space" like those on the ISS. They must be little spacecraft of their own providing life support and climate control for many hours. Some even came with their own attitude control and thrusting system (like the MMU of the early Shuttle days and SAFER systems - that must have been an astronauts dream to freely fly around with a MMU - the mother of all EVAs!). Size and mass and bulk do not matter much with this kind of suit, the astronauts mainly use their hands at work and the overall package must be safe and comfortrable to wear and work inside for a whole day.
And then there are the suits for lunar and planetary exploration. They are like EVA suits in many respects (life support, heating/cooling, communications) but they must be lightweigt and flexible enough to wear with gravity present. To this day there is not yet a good solution of how to build such a suit. The lunar suits of Apollo for example are much too heavy to be worn on Mars with it's higher gravity. But the demands on the life support on Mars (no atmosphere, extreme temperatures) are the same, so the backpack must contain the same stuff as those from the
time of Apollo. A difficult task!
And then of course, for longer stays on Moon and Mars, protection from ionising radiation will become an important task for the suits as well. Even more difficult to ensure.

Mars suit.

​​​​​​​https://en.wikipedia.org/wiki/Mars_s...ion%20sickness.

So all safely back on the ground. On to IFT5….