A bit off topic, but tar should only be used as temp repair to prevent further damage from water and moisture. For example its winter and you have asphalt shingle roof. Asphalt shingles are brittle when cold so attempting a proper repair could damage more shingles on what was a rather localized problem. Also ice and snow makes working on a roof more hazardous.

An other possible reason would be you don't have enough money on hand at the moment the issue was discovered giving you a few months to set asside enough money. Similar, thing the contractors schedule is packed so a quick temp repair can hold you off while you wait the week or two for his crew to begin work. An other similar issue is waiting on materials if your roof uses a material that is not locally stocked.

Tar also has a nasty problem of becoming brittle from UV light something roofs get plenty of. So instead of flexing under thermal expansion and contraction it just cracks. So its not ideal for anything but a temporary fix.

Now for choosing the most expensive contractor that is on your condo. Although they could have certainly been valid reasons.