A PNG is a raster file: a grid of coloured pixels, often with a transparent channel so a logo can sit on any background. SVG is a vector file. It stores shapes as coordinates and curves, not as a bitmap. A PNG to SVG conversion therefore has to redraw every edge.
Changing the extension, or wrapping the PNG inside an SVG with an image tag, keeps the pixels. Enlarge that file and the stairs come back; a cutter cannot follow it. Many free converters take exactly that shortcut, or follow every pixel with a single brightness threshold.
We run an AI tracer on the uploaded PNG, fit smooth curves to the colour areas, and write a standard SVG of filled paths. Transparent pixels stay empty. The watermarked preview is free; a clean PNG to SVG download costs 10 credits and includes EPS, PDF, DXF and PNG of the same trace.