Adjust register in games.

And Higemaru and Golvellius 2 were also released before Space Manbow.

In addition, documentation and programming utilities were hard to get in Europe. Programming on MSX2 required a lot of effort when they were less widespread than Commodores and many other machines. So developers just went for quick and dirty ports.

There is also the fact that you have to switch between two pages to do proper scrolling so we can only do that for MSXs with 128kB.

Games for Colecovision were no better. The Coleco ones were eye-catching to look like arcade games but they were short and therefore very repetitive due to lack of memory. On MSX, Konami also made cool graphics but focused more on gameplay and music. Konami has made few technically impressive games (only Firebird and Space Manbow).

they were better . I've never seen such a effort to emulate arcade games on titles born on msx. For example, i suspect that if Jungle hunt was not ported for colecovision too, but only for msx 1, the smooth scrolling would not be implemented and we got the usual 8x8 scrolling.
I think colecovision games were superior in terms of accuracy and effort and i think this can be due to some kind of more strictly control from colecovision over the titles for its machine

They look a lot better than the average msx games. For example, it not so common to see smooth scrolling on msx1 games, despite the same video hw. on msx we have often the usual 8 pixel blocky scrolling.
the fact that there are less stages is mainly due to the fact that coleco cartridges use to more usual memory amount that for example nemesis or gradious that can count on megarom size cartridges.

Even more impressive games like nemesis or gradius, are nothing special from the tech perspective:
- The usual nametable scrolling
- The usual sprite usage with the usual sprite-cycling routine.

Colecovision games, by contrast were in trying to achieve, for example the most arcade fidelty possible with MSX hw. It does require more effort trying to get smooth scrolling on a hw that does not support it, than simply staying with the features easily available and filling in a megarom a lot of game stages.

Pratically all coleco games were on average better than msx1 native games.

this is of course your opinion not an objective thing.
In reality, none of this games have a single thing that is not easily doable on MSX1. Instead they spot things that are common to pratically all msx games, Some do not scroll at all.

already done before.

Apparently? What they achieve is not an illusion! it's here and anyone can see this. We are talking of objective things not of personal interpretations!

In what they are richer? Because they managed to fit a lot of stages thanks to megarom size?
I do not define this a rich game, only a big game.
Different thing if one manage a way to get, for example a fast racing game with the usual arcade perspective, and a very fast road movement .
For example, take konami road fighter: it is a game that poses no challenge, it only have a bird view of the car, small sprites a blocky scroll etc. where is the value, ? can we say that ROAD FIGHER pushed the msx limits? NO, for sure. Pratically every developer could achieve this.
By contrast the MSXDEV XRacing Game is a true gem becauuse it achieve things rarely seen on a MSX1 racing game because relatively difficult, (smooth horizontal scrolling, very nice gfx, good gameplay)