You can't just plop several thousand colonists down on a world and expect them to pick up where their mother world left off.
Presuming the mother world or the Ministry of Colonization did a proper survey of the world, the colonists land on a site that meets several vital needs... clean water, land able to produce food, and within a reasonable distance to key basic resources [copper, iron, petroleum, etc].
The colonists spend the first couple years assembling the infrastructure necessary to support a civilization... homes, power, sewage, a data net, etc. By this point the mother world has sunk a lot of time and money into the colonial project. It understands that ongoing support is just as necessary as the initial funding was. They're willing to replace broken equipment, send food and engineers [some of whom will but most will not want to become colonists themselves] and so on. However, after a few years of happy vid-casts telling the mother world how great the colony is doing, they're gonna get bored with it. Every news blurb about the colony will remind them that that is where their taxes are going and they haven't seen any return for that money.
And right about the time the fusion plant and computers start to wear out, the mother world is gonna want to start seeing some return on its investment. And that means a fair percentage of the colonists are going to have to start working on resource extraction that does absolutely nothing to build the colony. All those resources are going back to the mother world to 'pay back' the whole colonial effort.
Let me point that all of this assumes nothing goes wrong... and something ALWAYS goes wrong. Even Star Trek's hunky-dory 'everything is fine' civilization faces problems when humans intrude on another planet's biosphere like a virus. Unknown sicknesses, environmental disasters, poor equipment, lousy planning, any one a million different things can and WILL go wrong on a project of this magnitude.
The end result is that the colony will [hopefully] build itself up to self-sustainability and then have to develop industries that manufacture goods the mother world wants at a reasonable enough rate of exchange that the colony can start to advance its own condition. And if they can't generate income for themselves, their technology WILL regress as high-tech items wear out. And this is perfectly normal and even expected in a colonial operation.