Why does a plant look worse at home than it did in the garden centre?
Because it was grown in conditions you cannot reproduce, and what you bought was a plant at an artificial peak rather than a plant in a stable state.
What commercial growing does to a plant:
Ideal light, warmth and humidity, maintained continuously in a glasshouse. Your windowsill is darker than it feels — human vision adapts, and indoor light is frequently a tiny fraction of outdoor levels.
Constant feeding, through irrigation water. The plant is growing at maximum rate and stops abruptly when that ends; potting compost typically holds only a few weeks of nutrients.
Growth regulators. Many flowering plants are treated with chemicals that produce compact, heavily flowering specimens. As it wears off the plant reverts to its natural habit, and people conclude they have ruined it.
Forcing. Bulbs and seasonal plants are manipulated with light and temperature to flower out of season, which is not repeatable at home.
Overplanting. Several plants are commonly potted together to look full — supermarket basil is the standard example, a dense clump of seedlings competing and collapsing within weeks. Splitting it into a few pots is the fix.
Why the move itself is a shock:
Acclimatisation. A plant moved to lower light sheds the leaves it can no longer support. Some leaf loss after purchase is normal and expected, not a failure.
Transport and shop conditions, which may have included cold, draughts or a week of drying out.
Immediate repotting, which people do straight away and which adds root disturbance to an already stressed plant. Wait a few weeks unless it is genuinely root-bound.
What actually helps: buy plants suited to the conditions you have rather than the ones you want; put them in the best light available and leave them there; start feeding after about six weeks; delay repotting; expect the first flush of flowers not to repeat; and judge a plant by the new growth it makes for you rather than by the growth it arrived with.